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J Halttunen

Publications and source records attributed to J Halttunen.

At least 55 records · Page 3Linked to original sources
PubMed1990

The frequency of B cells secreting antibodies against donor MHC antigens in rats rejecting renal allografts.

We have estimated the frequency of B cells secreting antibodies against donor MHC antigens in rats rejecting histoincompatible renal allografts. In a major plus minor antigen-incompatible DA-to-WF combination on day 4 post-transplantation, reverse protein A plaque assay demonstrated that in the graft the frequency of lymphoid cells secreting Ig was 1:850. A major locus-incompatible and minor locus-compatible, congeneic LBN-to-Lewis strain combination was then applied to estimate the specificity of the secreted antibody. The lymphoid inflammatory cells were fused with mouse myeloma cells, cultured under limiting dilution conditions, and assayed by ELISA to donor and irrelevant strain spleen cells. Among cells infiltrating the graft, the fusion frequency was 1:172 x 10(3) and the frequency of Ig-producing hybrids 1:400 x 10(3) (i.e., this assay was approximately three log orders less sensitive than the reverse pA assay). The frequency of hybridomas secreting specifics antibodies against donor MHC antigens was 1:720 x 10(3) (i.e., every second hybridoma deriving from inflammatory population produced specific Ig). In addition, there was at least one obviously polyspecific population of hybridomas, detectable only in the spleen and reactive with all rat strains tested with a frequency of 1:700 x 10(3). The inflammatory cells were also cultured directly under limiting dilution conditions, and the frequency of Ig-secreting cells was determined by ELISA. The frequency of inflammatory lymphocytes secreting detectable amounts of immunoglobulin in the supernatant was 1:14 x 10(3) in the graft (i.e., this assay was approximately one log order less sensitive than the reverse protein A plaque assay).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Properties of B cells and Thy-1-antigen-expressing cells infiltrating rat renal allografts.

We have examined (1) the frequency of B cells secreting antibodies against donor major histocompatibility complex (MHC) antigens and (2) the properties of Thy-1-antigen-expressing leukocytes in rats rejecting renal allografts. Our results show that B cells secreting antibodies are present in the inflammatory cell population at the frequency of 1:850. Among them only 1 out of 2-150 is engaged in production of antibodies directed to the graft MHC antigens, depending on the method of assay. This suggests that despite the observed significant production of nonspecific immunoglobulin in situ, only a minority of the B-cell population is specifically committed to the graft MHC antigens. This finding is concordant with the described previously low frequencies of the T cells specifically directed toward the graft MHC antigen. The role of the "immunologically noncommitted" cells in graft rejection is unknown. We have found that a substantial part (up to 60%) of inflammatory cells invading a rat kidney allograft express the Thy-1 antigen. This suggests that they might be immature (progenitor?) cells and, therefore, unable to respond to the graft antigens. Progenitor-like properties of these cells have been confirmed by their ability to reconstitute lethally irradiated syngeneic rat. Finally, these immature cells are of lymphoid, not of myeloid, linkage, because they do not proliferate in the presence of GM-CSF.

Animals↗
PubMed1990

Immunogenicity of rat renal allograft nephron components in vivo. Lack of correlation between MHC expression and immunogenic potential.

Cultured rat nephron components--i.e., tubular cells, glomerular mesangial cells, and glomerular epithelial cells--were compared with cultured rat heart endothelial cells for their in vivo immunogenicity using the primed rejection assay (PRA). Gamma-interferon (gIFN) was used to regulate the class I and class II MHC antigen expression of the cells tested. The heart endothelial cells proved to be the only cell type capable of inducing a maximal rejection response in the native state. This was achieved with a cell number of 10(6) when the survival of a subsequent heart allograft from a relevant donor was reduced from 5 to 3 days. All kidney nephron components proved to be immunogenic in PRA but to a far lesser extent than the endothelial cells. A reduction of graft survival from 5 to 4 days was achieved with a cell number of 10(6) cells, and no immunogenic effect (with the exception of mesangial cells contaminated by a small number of macrophages) was observed in smaller cell numbers. The gIFN-treated endothelial cells were more potent than untreated endothelial cells. They reduced the graft survival to 4 days with a cell number of 10(3) and caused a maximal reduction of the survival to 3 days with a cell number of 10(5). The nephron components failed to increase their immunogenicity after 3-day gIFN treatment, regardless of a high increase in their class I and class II expression rates. The study suggests that, in contrast to the endothelial cells, none of the nephron components are able to act as an antigen-presenting cell on their own.

Animals↗
PubMed1990

Failure of rat kidney nephron components to induce allogeneic lymphocytes to proliferate in mixed lymphocyte kidney cell culture.

Rat kidney glomerular mesangial, glomerular epithelial, and tubular epithelial cells were isolated in virtually pure form and studied in mixed lymphocyte kidney cell culture (MLKC) for their ability to induce allogeneic spleen lymphocyte proliferation. The responses were compared with proliferative responses induced by allogeneic endothelial cells or spleen lymphocytes in the same strain combination. Stimulator cells were treated or left untreated with gamma-interferon, known to increase the major histocompatibility complex class II (and class I) expression of the stimulator cells. The results demonstrate that the nephron components are not able to induce lymphoproliferation in the MLKC. In contrast, the endothelial cells of rat heart were potent inducers of lymphoproliferation in mixed lymphocyte endothelial cell cultures (MLEC), as were allogeneic spleen cells. Although the kidney parenchymal cells have been shown to be immunogenic in vivo, the present finding suggests that they are unable to function as antigen-presenting cells on their own.

Animals↗
PubMed1989

Local events in graft rejection.

It appears that allograft rejections can be considered as a series of cellular and molecular cascades of inflammation triggered by the immune response. In acute rejection, inflammatory changes with a prominent blast cell component dominate. The main result is toxic damage of several parenchymal components, particularly the microvascular endothelium, resulting in necrosis of the parenchyma and loss of the allograft within days after transplantation. In the chronic type of rejection, inflammation also exists, but the major manifestations are different. Adventitial inflammation and perivascular cuffing of leukocytes result in concentric intimal proliferation and atherosclerosis. Very little experimental data exist, at present, on the mechanisms of transplant atherosclerosis and chronic rejection.

Acute Disease↗
PubMed1988

Characteristics of dendritic cells in rat liver.

The properties of rat liver dendritic cells (DC) were analyzed after collagenase digestion of the tissue and enrichment with density gradient centrifugation. The liver macrophages (Kupffer cells) were eliminated by adherence before the gradient centrifugation. The morphology of isolated DC in May-Grunwald-Giemsa (MGG) stained cytocentrifuge preparations resembled that of monocytes with certain dissimilarities. The expression of major histocompatibility complex (MHC) class II antigens (Ia) on DC was analyzed with the Staphylococcus aureus rosette method using a monoclonal antibody. The binding of anti-Ia antibody to rat liver DC was 3 times stronger than to passenger lymphocytes and 10 times stronger than to hepatocytes. All DC were Ia-positive tested with indirect immunofluorescence technique, and none of them were able to phagocytize antibody-coated human red cells. The DC did not express intracytoplasmic lysozyme, or surface Fc-receptors, and they all were negative in alpha-naphtylacetate esterase (ANAE) staining. Thus, although the dendritic cells of rat liver seem to belong to the monocytic series according to morphologic criteria, they were all negative when tested for typical monocyte/macrophage markers. The immunocenic potential of DC was analyzed by testing their ability to prime a naive recipient for graft rejection. The number DC needed for the priming was comparable with the number of spleen lymphocytes needed for an equivalent effect, indicating that the DC were highly immunogenic. The hepatocytes showed practically no immunogenic effect. Thus the immunogenic potential of the tested cells, i.e. their ability to induce accelerated transplant rejection, carries a good correlation with the expression of Ia-antigens on the cell surface.

Animals↗
PubMed1987

Renal target structures in acute allograft rejection: a histochemical study.

With an aim to investigate the relative sensitivity of various renal structures to allograft rejection, we analyzed the histochemical reaction intensity of seven enzymes prominently displayed in various rat kidney components, and correlated the expression of these enzymes both to the degree of intra-graft inflammation and to the expression of class II MHC antigens in graft capillary endothelial cells. Syngeneic transplants and normal renal tissue were used as controls. At the peak of inflammation, on the fifth day after transplantation, adenosine triphosphatase activity of vascular endothelial cells was strongly reduced in the peritubular capillary endothelium of the allograft, moderately in the glomerular endothelium but very little in the endothelium of arteries and veins. Lactate dehydrogenase, succinate dehydrogenase, isocitrate dehydrogenase, alkaline phosphatase, acid phosphatase and glucose-6-phosphatase activities were moderately reduced in the proximal tubular cells of the allograft and even less in the distal tubular cells. The results suggest that the prime target of the host immune attack is the intertubular capillary endothelium, whereas the distal tubular cells are relatively insensitive to immune injury.

Acute Disease↗
PubMed1987

Allospecific rat-mouse T hybridoma clones generated from kidney graft-infiltrating cells.

In order to dissect the cellular mechanisms that lead to allograft rejection, infiltrating cells can be isolated and expanded in vitro for functional assays. Since the maintenance of these lines and clones is time-consuming, and large numbers of specific cells cannot be easily obtained, we fused the graft infiltrating cells, after in vitro specific expansion, with the murine T lymphoma BW5147. The rat-mouse TT hybridomas thus generated were screened for antigen-dependent interleukin 2 production, for antigen-dependent polyclonal helper activity, and for surface phenotype. The high frequency of specific clones obtained indicates that this is a convenient approach to generate alloreactive hybridoma clones with specific functions from the inflammatory infiltrates of rejected grafts.

Animals↗
PubMed1987

Impact of class II major histocompatibility complex antigen expression on the immunogenic potential of isolated rat vascular endothelial cells.

We have investigated the immunogenic potential of rat heart vascular endothelial cells by their ability to induce an accelerated rejection of a relevant heart allograft, and related the immunogenic potential to the expression of class II major histocompatibility complex (MHC) antigens on the endothelial cell surface. Only 12% of freshly isolated rat vascular endothelial cells express class II antigens in serum-free medium, and the level of expression is low as judged by immunoperoxidase staining and/or the ability of endothelial cells to bind staphylococci to the cell surface after treatment with monoclonal antibodies to the class II molecule. On the other hand, 99% of the endothelial cells under the same conditions express class I, and the level of expression is high. The class II antigen expression of vascular endothelial cells can be upregulated to more than 98% by recombinant gamma-interferon in vitro--and, concomitantly, the level of expression becomes high, even on the cell surface. Treatment with gamma-interferon did not substantially alter the level of class I expression. The endothelial cells expressing class II antigens weakly, are also weakly immunogenic in vivo: 10(7) endothelial cells are required to reduce the graft survival by 50% of that of the unprimed host. On the contrary, the endothelial cells of the same lineage induced to express class II antigens by gamma-interferon in vitro are highly immunogenic in vivo, as immunogenic as freshly-isolated spleen dendritic cells: only 10(4) endothelial cells are required to induce a 50% reduction of graft survival. These observations demonstrate for the first time that rat vascular endothelial cells are immunogenic in a primary transplantation response in vivo--and, moreover, that the immunogenic capacity of the endothelial cells is directly proportional to the extent of class II MHC antigen expression on the cell surface.

Animals↗
PubMed1987

Evidence that thymectomized, bone marrow-reconstituted rats do not reject their allografts.

We have investigated the reasons why thymectomized, bone marrow-reconstituted (B) rats do not reject their allografts, by comparing the structure of inflammation and functions of inflammatory cells in nonrejecting allografts to rejecting allografts in normal control recipients. The results demonstrate that B recipients mount a specific cellular response towards the graft. The response in B recipients differs from that in normal controls by a smaller intensity of inflammation, fewer blast cells, and activated mononuclear phagocytes in the inflammatory infiltrate, as well as a delay in the appearance of specific donor-directed lytic activity in the graft. B rats also have fewer blast cells and an inverted CD4/8 ratio in the spleen. There is no obvious absence of any given cell type or cellular function in the graft inflammatory infiltrate. In light of these results no cell type responsible for allograft nonrejection can be pinpointed.

Animals↗
PubMed1987

Mobile blood-derived components in rat renal allograft contain significant immunogenic potential.

Using a modified 'primed rejection assay' (PRA), we have investigated the immunogenic potential of different rat renal allograft components. Temporary transplantation of an extensively perfused DA kidney to a WF recipient can sensitize the WF recipient in less than 10 min; consequently, the survival of a subsequent DA heart allograft is significantly reduced. Irradiation of the renal allograft donor significantly reduces the immunogenic potential of the first allograft, but does not deplete it entirely. When the first allograft was made chimeric with regard to the (capillary) blood compartment, it was found that in vivo perfusion of an irradiated DA kidney with WF blood did not alter the immunogenic potential in WF recipients, whereas perfusion of irradiated DA kidneys with DA blood increased the immunogenicity. On the other hand, short in vivo perfusion of irradiated WF kidneys with DA blood make the first WF kidney allograft strongly immunogenic in the WF recipient, whereas perfusion of the kidney with WF blood has no effect. The rapid rate of sensitization observed, coupled with the induction and alteration of the allograft immunogenic potential by manipulation of blood-derived capillary compartment, suggests that mobile blood-derived components, which are outside the reach of extensive perfusion, contain significant immunogenic potential.

Animals↗
PubMed1987

Frequency and functional characterization of specific T-helper cells infiltrating rat kidney allografts during acute rejection.

T-helper cells (ThC) play an important role in the induction of both cytotoxic T-cell responses and B-cell responses against the grafted organ. Furthermore, ThC alone are capable of causing graft rejection in T cell-deprived mice and rats. In view of these observations we found it important to analyse the frequency and functions of donor-specific ThC in the allograft and in the recipient lymphoid system during the course of acute renal allograft rejection. A limiting dilution assay was developed which, due to the absence of exogenous interleukin 2 (IL-2) and the low numbers of stimulator cells used, appears to be highly selective for the proliferation of specific ThC. Kidney transplants were performed from LBN (RT1n) to congenic Lewis (RT1l) strain differing in major histocompatibility complex (MHC) only. The inflammatory (white) cells were recovered from the graft, and blood and recipient spleen and the frequency of RT1n-responding ThC were determined at different times after transplantation. In the kidney graft itself, the frequency of ThC responding to RT1n MHC antigens was 1:3000 on day 2 and increased to 1:670-1320 at the peak of inflammation. In the spleen, the frequency increased from 1:1000 on day 0 to 1:200 on day 8, and remained high even after the graft was rejected. In the blood, the frequency stayed at the 1:400-1:800 level, and increased to 1:200 only after the graft had been completely destroyed. Individual ThC clones deriving from limited dilution assays of kidney and spleen cells were recovered and expanded with irradiated donor cells without IL-2 and finally with exogenous IL-2 only. All clones showed the T-helper (W3/25) phenotype, seven out of eight tested clones showed a specific anamnestic response to RT1n alloantigens and no response to RT1l or RT1a in a secondary MLC, 12 out of 12 clones produced IL-2 and 11 out of 11 clones produced gamma interferon upon re-stimulation with relevant allogeneic cells, and eight out of ten clones collaborated with syngeneic B cells for Ig synthesis, indicating that they were indeed derived from specific ThC and/or from their precursors. Taken together, the results demonstrate that specific ThC and/or their precursors represent only a very small minority in the graft-infiltrating inflammatory population. This makes it most unlikely that the ThC themselves are responsible for graft destruction; the results indicate rather that a major role of ThC in situ may be instruction of immunologically specific and nonspecific components of inflammation.

Animals↗