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PubMed2005

Heterogeneity of growth hormone immunoreactivity in lymphoid tissues and changes during ontogeny in domestic fowl.

Growth hormone (GH) expression is not confined to the pituitary and occurs in many extrapituitary tissues. Here, we describe the presence of GH-like moieties in chicken lymphoid tissues and particularly in the bursa of Fabricius. GH-immunoreactivity (GH-IR), determined by ELISA, was found in thymus, spleen, and in bursa of young chickens, but at concentrations <1% of those in the pituitary gland. Although the GH concentration in the spleen and bursa was approximately 0.82 and 0.23% of that in the pituitary at 9-weeks of age, because of their greater mass, the total GH content in the spleen, bursa, and in thymus were 236, 5.18, and 31.5%, respectively, of that in the pituitary gland. This GH-IR was associated with several proteins of different molecular size, as in the pituitary gland, when analyzed by SDS-PAGE under reducing conditions. While most of the GH-IR in the pituitary was associated with the 26 kDa monomer (40%), the putatively glycosylated 29 kDa variant (16%), the 52 kDa dimer (14%) and the 15 kDa submonomeric isoform (16%), GH-IR in the lymphoid tissues was primarily associated (27-36%) with a 17 kDa moiety, although bands of 14, 26, 29, 32, 37, 40, and 52 kDa were also identified in these tissues. The heterogeneity pattern and relative abundance of bursal GH-IR bands were determined during development between embryonic day 13 (ED13) and 9-weeks of age. The relative proportion of the 17 kDa GH-like band was higher (45-58%) in posthatched birds than in the 15 and 18-day old embryos (21 and 19%, respectively). The 26 kDa isoform was minimally present in embryos (<4% of total GH-IR) but in posthatched chicks it increased to 12-20%. Conversely, while GH-IR of 37, 40, and 45 kDa were abundantly present in embryonic bursa ( approximately 30% at ED13 and approximately 52-55% at ED15 and ED18, respectively), in neonatal chicks and juveniles they accounted for less than 5%. These ontogenic changes were comparable to those previously reported for similar GH-IR proteins in the chicken testis during development. In summary, these results demonstrate age-related and tissue-specific changes in the content and composition of GH in immune tissues of the chicken, in which GH is likely to be an autocrine or paracrine regulator.

Animals↗

PubMed1991

Interferon gamma (IFN-gamma) production by gut-associated lymphoid tissue and spleen following oral Salmonella typhimurium challenge.

Although IFN-gamma has been shown to play an important role in protection against a systemic S. typhimurium challenge, the in vivo and in vitro production of this cytokine following S. typhimurium infection of the gastrointestinal tract has not been investigated. In this study, IFN-gamma production by gut-associated lymphoid tissue and spleen was investigated in mice following oral challenge with S. typhimurium. Cells obtained from the Peyer's patches (PP), mesenteric lymph nodes (MLN) and spleen (Sp) of mice orally challenged with S. typhimurium were assessed for levels of IFN-gamma mRNA after varying times following in vivo infection. RNA obtained from the above tissues was subjected to reverse transcription followed by PCR amplification using primers specific for murine IFN-gamma. Elevated levels of IFN-gamma mRNA were first detected in the PP at 6 h post-challenge. Elevated levels of IFN-gamma mRNA were then detected in the MLN at 24 h and in the spleen at 4 days post-challenge. These in vivo results were in agreement with the ability of these lymphoid tissues to produce IFN-gamma upon in vitro stimulation with killed S. typhimurium. Neutralization of endogenously produced IFN-gamma by administration of mAb to IFN-gamma completely abrogated resistance to an oral challenge of S. typhimurium. A significant difference in the percent mortality was observed between the antibody-treated and control groups. Evaluation of bacterial spread in the antibody treated group versus the control group at 4 days following oral challenge revealed higher numbers of bacteria in the spleen and liver of antibody treated mice. These results clearly show that IFN-gamma is rapidly produced by gut-associated lymphoid tissue and spleen following oral S. typhimurium infection, and that endogenous production of IFN-gamma is essential in host resistance to S. typhimurium.

Administration, Oral↗

PubMed1975

Unique cathepsin D-type proteases in rat thoracic duct lymphocytes and in rat lymphoid tissues.

Two unique cathepsin D-type proteases apparently present only in rat thoracic duct lymphocytes and in rat lymphoid tissues are described. One, termed H enzyme, has an apparent molecular weight of similar to95,000; the other, termed L enzyme, has an apparent molecular weight of similar to45,000, in common with that of most cathepsins D from other tissues and species. Both enzymes differ from cathepsin D, however, by a considerably greater sensitivity to inhibition by pepstatin and by a smaller degree of inhibition by an antiserum which inhibits rat liver cathepsin D. H enzyme is converted to L enzyme by treatment with beta-mercaptoethanol; the relationship between the two enzymes remains unknown. H and L enzyme have been detected in rat lymphoid tissues and in mouse spleen, but they are not present in other rat tissues (liver, kidney, adrenals), rabbit tissues, calf thymus, bovine spleen, or human tonsils. As measured on acid-denatured bovine hemoglobin as substrate, both enzymes have pH activity curves identical with that of rat liver cathepsin D, with optimal activity at pH 3.6. Activity on human serum albumin is much less and also shows an optimum at pH 3.6; hence, neither enzyme has the properties of cathepsin E. Thiol-reactive inhibitiors have no effect on the activity of H and L enzyme; thus they do not belong to the B group of cathepsins. Additional information, discussed in this paper, leads us to conclude that partially purified H and L enzymes are cathepsin D-type proteases.

Adrenal Glands↗

PubMed1992

Primary B-cell gastric lymphomas of mucosa-associated lymphoid tissue. Histological and immunohistochemical study of ten cases on surgical specimens.

Ten cases of gastric mucosa-associated lymphoid-tissue B-cell lymphoma were studied on surgical specimens by histology and immunohistochemistry, with monoclonal and polyclonal antibodies for B- and T-cells. For the first time, percentage of centroblast-like cells was appreciated, using their LN1 positivity, by opposition to the negativity of centrocyte-like cells (LN2 immunoreactivity alone). Lymphomas were divided into four main groups: A) centrocyte-like cells; B) centrocyte-like cells and immunocytoma; C) centrocyte-like cells admixed to centroblast-like cells; and D) centrocyte-like cells, immunocytoma and at least 30% of centroblast-like cells. Group C was divided into 3 subgroups: C1 (rare centroblast-like cells); C2 (30-50% of centroblast-like cells); and C3 (predominant centroblast-like cells). Therefore low grade (A, B, C1) and high grade malignancy groups (C2, C3, D) were identified: this preliminary subdivision could be extended in larger series and applied to mucosa-associated lymphoid-tissue lymphoma from other sites. Furthermore, the possible prognostic significance of this subdivision could be evaluated by correlation with long term follow-up.

Antigens, CD↗

PubMed1981

Presence of a complete endothelial barrier between lymph and lymphoid tissue in the lumbar lymph nodes of the duck (Anas platyrhynchos).

The ultrastructure of the lumbar lymph nodes of the domestic duck is described and compared with published accounts of mammalian lymph nodes. The barrier to cell migration between lymphoid tissue and lymph is more formidable in the duck than in the mammal. In the duck the lymphatic endothelium lining the lymph spaces is continuous and bonded with desmosomes whereas in the mammal it is unbonded and fenestrated. In both types of node there are filtering zones and areas of dense lymphatic tissue but their topographical organisation differs. There is no cortex or medulla in the duck lymph node and filtration occurs in extensive lymphatic spaces traversed by numerous trabeculae to which are attached rounded phagocytic macrophages. Dense lymphoid tissue is scattered throughout the node, suspended by trabeculae or attached to the capsule and there are blood vessels analogous to the post capillary venules of mammalian nodes where lymphocytes migrate between blood and lymphoid tissue.

Animals↗

PubMed2002

[Histological study of conjunctiva-associated lymphoid tissue in mice].

PURPOSE: To investigate conjunctiva-associated lymphoid tissue (CALT) in mouse conjunctiva. METHOD: We examined normal mice, ranging in age from 4 to 6 weeks, to investigate the presence of follicular tissue histologically. Next, we treated mice by topical instillation of ovalbumin and cholera toxin B, and then examined conjunctival follicles by immunohistological methods. RESULTS: Follicular tissue was present at the nictitating membrane. Both size and amount of follicular tissue was increased by the topical ovalbumin treatment. Immunohistological examination revealed CD4, CD8, and S-100 protein positive cells in follicular tissue. The epithelial layer, corresponding to follicular tissue, had intraepithelial pockets and CD4 positive cells in the pockets. CONCLUSION: It was concluded that the follicular tissue at the nictitating membrane is CALT in mice.

Animals↗

PubMed1989

Conjunctiva-associated lymphoid tissue (CALT) in normal and Bordetella avium-infected turkeys.

Conjunctiva-associated lymphoid tissue (CALT) was characterized in normal and Bordetella avium-infected turkey poults during the first 5 weeks of life. At 1, 5, 12, 19, 25, and 33 days post-hatching (DPH), upper and lower eyelids were examined by gross, histologic, and electron microscopic techniques. CALT was confined to the proximal part of the lower eyelid near the conjunctival fornix; it appeared by 5 DPH as individual lymphoid nodules and as dense masses by 19 DPH. In the upper eyelid, CALT was present only as isolated nodules. Histologically, CALT was composed of dense lymphocyte infiltrates within subepithelial connective tissue, intraepithelial lymphocytes, and flattened lymphoid-associated epithelium that lacked goblet cells. Germinal centers were in CALT by 19 DPH. By scanning electron microscopy, epithelial cells over lymphoid areas were flat and had short, irregular microvilli; non-lymphoid areas were covered by cells with tall, regular microvilli. Transmission electron microscopy revealed that with increasing age of birds, the epithelium over conjunctival lymphoid infiltrates became progressively flattened and infiltrated by lymphocytes. Some blood vessels in CALT had high endothelial cells; lymphocytes were in the lumen and between or beneath endothelial cells. In B. avium-infected poults, CALT was increased, developed earlier, and contained more germinal centers than in normal poults. We conclude that CALT of turkeys closely resembles other mucosal lymphoid tissues and may serve as a site for local antigen uptake.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Histological study of conjunctiva-associated lymphoid tissue in mouse.

PURPOSE: To investigate conjunctiva-associated lymphoid tissue (CALT) in the mouse conjunctiva by histological methods. METHODS: The presumed follicular tissue in the conjunctiva of normal mice, age ranging from 4 to 6 weeks, was histologically investigated by the hematoxylin-eosin staining method. Next, we treated the mice with topical instillation of a combined solution of ovalbumin and cholera toxin B to investigate the morphological changes of conjunctival follicles to antigen challenge. The treated mice underwent sequential clinical examinations, and the conjunctival follicular tissue was examined by an immunohistochemical method using anti-CD4 antibody, anti-CD8 antibody, and anti-S-100 antibody. RESULTS: Follicular tissue was present on the mouse nictitating membrane. Both size and number of follicular tissue areas increased with topical ovalbumin treatment. Immunohistochemical study revealed CD4, CD8, and S-100 positive cells in the follicular tissue. The epithelial layer, corresponding to follicular tissue, demonstrated intra-epithelial pocket and the presence of CD4-positive cells in the intra-epithelial pocket. CONCLUSION: Follicular tissue at the nictitating membrane is CALT in the mouse.

Animals↗

PubMed1998

The lymphotoxin beta receptor controls organogenesis and affinity maturation in peripheral lymphoid tissues.

Lymphotoxin beta receptor (LTbetaR)-/- mice were created by gene targeting. LTbetaR-/- mice lacked Peyer's patches, colon-associated lymphoid tissues, and all lymph nodes. Mucosa patrolling alphaEbeta7high integrin+ T cells were virtually absent. Spleens lost marginal zones; T/B cell segregation and follicular dendritic cell networks were absent. Peanut agglutinin+ cells were aberrantly detectable around central arterioles. In contrast to TNF receptor p55-/- mice, antibody affinity maturation was impaired. Since LTbetaR-/- mice exhibit distinct defects when compared to LTalpha-/- and LTbeta-/- mice, it is suggested that the LTbetaR integrates signals from other TNF family members. Thus, the LTbetaR proves pivotal for the ontogeny of the secondary lymphoid tissues. Furthermore, affinity maturation is dependent on LTalpha1beta2 rather than on LTalpha3.

Animals↗

PubMed1977

Estimation of the migration of thoracic duct lymphocytes to non-lymphoid tissues. A comparison of the distribution of radioactivity at intervals following i.v. transfusion of cells labelled with 3H, 14C, 75Se, 99mTc, 125I and 51Cr in the rat.

The distribution of radioisotopes in tissues was measured following i.v. injection of labelled thoracic duct lymphocytes into syngeneic rats. The rate of elution of an isotope from the labelled cells and the subsequent fate of the eluted isotope were shown to be the most important factors limiting the usefulness of such isotopes for measuring cell localization particularly in non-lymphoid tissues. Comparison of labelling procedures using [3H] and [14C]uridine, [3H] and [14C]leucine, [75Se]-L-selenomethionine, [99mTc]sodium pertechnetate and [51Cr]sodium chromate in vitro and [3H]thymidine in vivo showed that 51Cr had the fewest disadvantages in the present context. Using 51Cr-labelled cells, the radioactivity was measured in a wide range of non-lymphoid tissues, and estimates of cell traffic were obtained. In skin, for example, the results indicate a cell flux in the range of 10(4)-10(5) lymphocytes/gm/hr. Evidence is presented which suggests that the early substantial localization of labelled cells in the lung is not an artefact due to sequestration or embolization of traumatized cells but probably reflects a slow intravascular transit time through this capillary bed. The primary lymphoid organs, thymus and bone marrow were shown to include a subpopulation of lymphocytes which belong to the recirculating pool. The thymus always contained a greater concentration of radioactivity at 24 hr than all non-lymphoid tissues except liver and kidney (approx. 0-1% of the recirculating lymphocyte pool) and the bone marrow was capable of temporarily accepting a substantial proportion (approx.25%) of the injected cells.

Animals↗

PubMed2004

Activation of NF-kappaB and inhibition of p53-mediated apoptosis by API2/mucosa-associated lymphoid tissue 1 fusions promote oncogenesis.

Mucosa-associated lymphoid tissue (MALT) lymphoma is the most common extranodal lymphoid cell neoplasia; it frequently follows chronic bacteria-induced inflammation in various tissues. MALT lymphomas are characterized genetically by the t(11;18)(q21;q21) translocation, which yields chimeric transcripts encoding structurally distinct API2/MALT1 fusion proteins. In this study, we provide functional evidence for the contribution of API2/MALT1 fusion proteins to transformation of cells in culture by activating the NF-kappaB pathway through a RelB/p50 dimer. Using microchip gene expression analysis, we demonstrate that different forms of the API2/MALT1 proteins activate both unique and overlapping gene programs in cells. In addition to this genome reprogramming, expression of distinct API2/MALT1 fusion products inhibits DNA damage-induced, p53-mediated apoptosis in an NF-kappaB-dependent manner. Collectively, these data reveal previously unknown functional diversity among API2/MALT1 fusion products and their function in NF-kappaB signaling as it connects to the apoptotic program, a pathway with strong relevance to cancer. Furthermore, they provide evidence underlying the emerging role of the NF-kappaB signaling pathway in the inhibition of apoptosis.

Animals↗

PubMed2000

BCL10 expression in normal and neoplastic lymphoid tissue. Nuclear localization in MALT lymphoma.

BCL10 is an apoptotic regulatory molecule identified through its direct involvement in t(1;14)(p22;q32) of mucosa-associated lymphoid tissue (MALT) lymphoma. We examined BCL10 protein expression in various normal tissues and B-cell lymphomas by immunohistochemistry of formalin-fixed and paraffin-embedded tissues using mouse BCL10 monoclonal antibodies. BCL10 protein was expressed in lymphoid tissue but not in 21 various other tissues with the exception of breast. In normal B-cell follicles, the protein was expressed abundantly in the germinal center B cells, moderately in the marginal zone, but only weakly in the mantle zone B cells. Irrespective of their stage of B-cell maturation, BCL10 was predominantly expressed in the cytoplasm. In contrast, each of the four MALT lymphomas with t(1;14)(p22;q32) showed strong BCL10 expression in both the nucleus and cytoplasm. Twenty of 36 (55%) MALT lymphomas lacking the translocation exhibited BCL10 expression in both the nucleus and cytoplasm although at a much lower level, whereas the remaining 16 cases displayed only cytoplasmic BCL10. Unlike MALT lymphoma, both follicular and mantle cell lymphomas generally displayed BCL10 expression compatible to their normal cell counterparts. Our results show differential expression of BCL10 protein among various B-cell populations of the B-cell follicle, indicating its importance in B-cell maturation. The subcellular localization of BCL10 was frequently altered in MALT lymphoma in comparison with its normal cell counterparts, suggesting that ectopic BCL10 expression may be important in the development of this type of tumor.

Adaptor Proteins, Signal Transducing↗

PubMed1993

Stimulation of antigen-specific T- and B-cell memory in local as well as systemic lymphoid tissues following oral immunization with cholera toxin adjuvant.

In the present study we investigated immunological memory at the cellular level following oral immunization using cholera toxin (CT) as the mucosal adjuvant. We found that memory cells, isolated from mice orally primed with keyhole limpet haemocyanin (KLH) admixed with CT adjuvant 8 months earlier, responded by increased proliferation to antigen-challenge in vitro. In contrast, unstimulated memory cells or KLH-stimulated cells from naive mice did not respond. Memory cells were isolated from different lymphoid tissues; spleen (SP), mesenteric lymph nodes (MLN), Peyer's patches (PP) as well as the intestinal lamina propria (LP). Thus, oral immunization using CT adjuvant promoted the generation of memory cells that were present in both systemic and local intestinal lymphoid tissues. The demonstration of lymphokine production in the KLH-responsive cultures indicated the presence of antigen-specific memory T cells. Lymphokine production early in culture was dominated by interleukin-2 (IL-2), which peaked on day 2-3, followed by IL-5 and, in particular, interferon-gamma (IFN-gamma) which increased over time. Lamina propria memory cells were found to proliferate poorly to recall antigen in vitro compared to lymphocytes from SP or MLN. In contrast, very significant production of IL-5 and, in particular, IFN-gamma was demonstrable in LP cell cultures. The use of CT adjuvant also stimulated the generation of antigen-specific memory B cells following oral immunization. This was evidenced by KLH-specific antibody production in antigen-challenged memory lymphocyte cultures. The memory B cells produced IgM anti-KLH, while no detectable antigen-specific IgG or IgA was found. Unstimulated memory cells or naive cells failed to produce anti-KLH antibodies. These in vitro findings provide evidence that oral immunization using CT adjuvant stimulates both antigen-specific memory T and B cells. Furthermore, our data suggest the existence of memory B cells following oral CT adjuvant immunization which have retained the ability to produce IgM and which therefore probably have not undergone terminal isotype switch differentiation to other isotypes and thus have not deleted the mu constant heavy-chain gene. Finally, our data also suggest that memory T and B cells, either sessile in the various lymphoid tissues or recirculating, can be activated by antigen in situ in, for example, lymph nodes and spleen and, more importantly, in the intestinal LP itself.

Adjuvants, Immunologic↗

PubMed1992

Study of bronchus-associated lymphoid tissue in patients with diffuse panbronchiolitis.

Bronchus-associated lymphoid tissue (BALT) is thought to affect local immunologic defense mechanisms. Studies of BALT, however, have mainly been focused on animals, and information detailing the BALT structure and functions in humans is scanty. Therefore, the purpose of this study is to clarify BALT morphology and immunologic findings in patients with diffuse panbronchiolitis (DPB) and compare them with BALT findings in animals. Thus, in 17 patients diagnosed with DPB, open-lung biopsy specimens were reviewed, and lymphoid follicles with a lymphoepithelium that was determined as BALT were identified in 12 patients. BALT was found mostly at bifurcations from nonrespiratory bronchioles to respiratory bronchioles. This lymphoepithelium was devoid of cilia and was diffusely infiltrated with CD4-positive (helper/inducer) T cells. The majority of T cells were confined to the parafollicular area with a predominance of helper T cells. Also, a few high endothelial venules were recognized in the parafollicular area. Further, in a follicular area situated in the center of the BALT, a number of sigM-positive cells were found to be heavily distributed, suggesting that this follicular area has the characteristics of a B cell zone equivalent to a germinal center of the peripheral lymph nodes. These observations are comparable with BALT findings in animals and suggest that BALT is at least partially related to the local immune response.

Adult↗

PubMed2001

Vascular-associated lymphoid tissue (VALT) involvement in aortic aneurysm.

Vascular-associated lymphoid tissue (VALT) consisting of accumulations of immunocompetent and antigen presenting cells has recently been recognised in the arterial wall. In this study, we investigated the involvement of VALT in immune responses in abdominal aortic aneurysms (AAAs). Tissue samples were collected during operations from 31 patients with atherosclerotic infrarenal abdominal aortic aneurysms ranging in diameters from 5 to 8 cm. The specimens were immediately frozen and examined using single and double immunohistochemical staining. T-cell subpopulations, B-cells, dendritic cells and macrophages were identified using cell type specific antibodies. Cell contacts were examined by electron microscopy. Most inflammatory infiltrates were found in the adventitia. T-cells were the predominant cell type in a majority of inflammatory infiltrates but in seventeen cases, typical lymphoid follicles with B-cells forming germinative centres were also observed. In eight cases, the lymphoid follicles aggregated in lymph node-like structures. Dendritic cells were present within all inflammatory infiltrates and contacted lymphocytes. The present observations show that in aortic aneurysm, VALT is involved in immune responses and its activation mostly occurs in the adventitia. The formation of lymphoid follicles and lymph node-like structures in the adventitia suggests that VALT might locally serve the entire complex of both cellular and humoral immune responses in the aneurysmal wall.

Aged↗

PubMed1999

The requirement of membrane lymphotoxin for the presence of dendritic cells in lymphoid tissues.

Although several cytokines, including tumor necrosis factor (TNF), can promote the growth of dendritic cells (DCs) in vitro, the cytokines that naturally regulate DC development and function in vivo have not been well defined. Here, we report that membrane lymphotoxin (LT), instead of TNF, regulates the migration of DCs in the spleen. LTalpha(-/-) mice, lacking membrane LTalpha/beta and LTalpha(3), show markedly reduced numbers of DCs in the spleen. Unlike wild-type mice and TNF(-/-) mice that have densely clustered DCs in the T cell zone and around the marginal zone, splenic DCs in LTalpha(-/-) mice are randomly distributed. The reduced number of DCs in lymphoid tissues of LTalpha(-/-) mice is associated with an increased number of DCs in nonlymphoid tissues. The number of splenic DCs in LTalpha(-/-) mice is restored when additional LT-expressing cells are provided. Blocking membrane LTalpha/beta in wild-type mice markedly diminishes the accumulation of DCs in lymphoid tissues. These data suggest that membrane LT is an essential ligand for the presence of DCs in the spleen. Mice deficient in TNF receptor, which is the receptor for both soluble LTalpha(3) and TNF-alpha(3) trimers, have normal numbers of DCs. However, LTbetaR(-/-) mice show reduced numbers of DCs, similar to the mice lacking membrane LT alpha/beta. Taken together, these results support the notion that the signaling via LTbetaR by membrane LTalpha/beta is required for the presence of DCs in lymphoid tissues.

Animals↗

PubMed2003

Immunohistochemical characterisation of PCV2 associate lesions in lymphoid and non-lymphoid tissues of pigs with natural postweaning multisystemic wasting syndrome (PMWS).

The lymphoid, renal, pulmonary, and hepatic lesions of naturally occurring postweaning multisystemic wasting syndrome (PMWS) affected pigs have been studied by means of immunohistology. Ten conventionally reared pigs showing acute clinical signs of PMWS were selected from a farm on which animal were seronegative to porcine reproductive and respiratory virus and to Aujeszky's disease virus. All pigs were positive in tests for porcine circovirus type 2 by ISH and IHC. Monoclonal and polyclonal antibodies to CD3, CD79alpha, CD45RA (3C3/9), lysozyme, SLA-II-DQ (BL2H5), and MAC387 were used to characterise cells in PMWS lesions. The most relevant changes were reduction or loss of B and T lymphocytes, increased numbers of macrophages, and partial loss and redistribution of antigen presenting cells throughout lymphoid tissues compared to uninfected controls. The characteristics of lymphoid lesions in the present study strongly suggest an immunosuppressive effect of PMWS in affected pigs.

Animals↗

PubMed1994

Ostertagia ostertagi: changes in lymphoid populations in the local lymphoid tissues after primary or secondary infection.

The purpose of this study was to begin to define the changes in the local lymphoid tissues that accompany Ostertagia ostertagi infection in naive and immunized calves. Abomasal lymph nodes were taken from calves beginning as early as 2 days post-infection. Phenotypic changes in the resulting lymphocyte populations were assessed by flow cytometry utilizing monoclonal antibodies specific for the cell surface determinates CD2, CD4, and CD8. Changes in antigen specificity were determined by limiting dilution analysis utilizing antigen derived from fourth-stage O. ostertagi. Primary infection of naive calves caused a rapid 30-40% decrease in the percentage of T cells in the abomasal lymph nodes. This decrease in T cell percentage was due to a decrease in cells bearing the CD4 marker, a marker usually associated with helper T cells. Immunized calves were able to maintain normal T cell percentages of 50-60% for the first 5 weeks of infection. Immunization greatly increased the total number of Ostertagia-specific T cells in the abomasal lymph nodes owing to a marked increase in the size of the lymph nodes. Challenge infection of naive and immunized calves caused an increase in the frequency of parasite-specific T cells in both groups, but the increase was more rapid in the previously immunized calves. Within 5 weeks of infection, Ostertagia-specific cells could not be detected in the abomasal lymph nodes. These results indicate that the critical time period for expansion and regulation of Ostertagia-specific T cells in infected calves is early in the infection at a time that coincides with larval development. In addition, previous exposure to parasite antigens appears to result in more rapid responses and in the maintenance of normal ratios of T cell subpopulations in the draining lymphoid tissues.

Abomasum↗