Biomedical subjects

J Forman

Publications and source records attributed to J Forman.

At least 55 records · Page 3Linked to original sources

PubMed1995

Definitive identification of a gene that confers resistance against Toxoplasma cyst burden and encephalitis.

Control of resistance to cyst burden following per-oral infection with Toxoplasma gondii has been mapped previously to a region of mouse chromosome 17 of approximately 140 kb. This region is contiguous with and contains the class I gene, Ld. Resistance to development of toxoplasmic encephalitis has also been reported to be controlled by genes in this region of H-2. TNF-alpha, D and L genes, as well as unidentified genes, are also in this region. The work described here was performed to identify definitively the gene(s) in this 140 kb region that confers resistance to cysts and encephalitis. The study demonstrates that relative resistance to T. gondii organisms and cyst burden in brain, and toxoplasmic encephalitis, 30 days following per-oral T. gondii infection is correlated absolutely with the presence of the Ld gene in inbred, recombinant, mutant and C3H.Ld transgenic mice. Mice with the Ld gene had lower cyst burdens and less encephalitis than those without the Ld gene. Specifically, 30 days after infection mice with the Ld gene had minimal perivascular inflammation and meningeal inflammation and very few Toxoplasma cysts or organisms in immunoperoxidase-stained preparations of their brains. Mice without the Ld gene had a similar pattern of inflammation, but in addition they had collections of inflammatory cells in the brain parenchyma. Free tachyzoites were found within these foci of inflammation and cysts were present in these areas as well as in contiguous areas without inflammatory cells. There were CD4+ and CD8+ T lymphocytes in the areas of inflammation and throughout the brain parenchyma. Mice that were resistant to cysts and encephalitis had little detectable brain cytokine mRNA expression, while mice that were susceptible had elevated levels of mRNA for a wide range of cytokines, consistent with their greater amounts of inflammation. The present work definitively demonstrates that a Ld-restricted response decreases the number of organisms and cysts within the brain and thereby limits toxoplasmic encephalitis and levels of interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), interleukin-2 (IL-2), IL-6, IL-10, transforming growth factor-beta (TGF-beta), IL-1 alpha, IL1 beta and macrophage inhibiting protein (MIP) mRNA in the brain 30 days after per-oral infection.

Animals↗

PubMed1994

Identification of a Tap-dependent leader peptide recognized by alloreactive T cells specific for a class Ib antigen.

Recognition of the class Ib antigen Qa-1 by a portion of alloreactive cytotoxic T lymphocyte (CTL) clones requires that the target cell express a second gene, termed Qa-1 determinant modifier (Qdm). We show that Qdm is identical to most D allele genes, excepting Dk, and that a nonamer peptide derived from D alloantigens restores CTL recognition on cells that lack the Qdm-encoded determinant. The equivalent Dk peptide has an Ala-->Val interchange at P3 and requires approximately 4 logs more peptide than the AlaP3 peptide for target cell lysis. Two of five CTL clones, not dependent on Qdm for target cell recognition, also recognize the Qdm peptide as well as the ValP3 variant. Although the Qdm peptide spans residues 3-11 from the leader, it requires the Tap transporters for its expression. Thus, the response against this class Ib molecule provides a tool for dissecting alloreactivity as well as pathways for antigen presentation.

Amino Acid Sequence↗

PubMed1994

Positive selection of self- and alloreactive CD8+ T cells in Tap-1 mutant mice.

Mice with a homozygous deletion in their Tap-1 gene (-/- mice) express very low levels of cell membrane major histocompatibility complex class I molecules and have < 1% peripheral CD8+ T cells. We show that these -/- mice but not their +/- littermates display strong primary syngeneic anti-H-2Kb and -Db-specific responses mediated by CD8+ T cells. These responses are augmented by in vivo priming. Further, -/- mice primed in vivo with H-2d alloantigens generate an anti-H-2d response which appears nearly as strong as that found in +/- littermates. Both -/- anti-H-2b and anti-H-2d T cells do not recognize target cells from Tap-1 -/- animals or Tap-2-deficient RMA-S cells. Thus, some CD8+ anti-self and alloreactive T cells can be selected in the absence of Tap proteins.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1994

Natural killer cells recognize common antigenic motifs shared by H-2Dd, H-2Ld and possibly H-2Dr molecules expressed on bone marrow cells.

Murine natural killer (NK) cells can mediate specific rejection of bone marrow cell (BMC) allografts. Whereas positive recognition of allogeneic MHC antigens forms the basis for T cell alloreactivity, it has been postulated that NK cells are reactive against targets that do not express certain self-encoded MHC class I antigens. Here, we study the immunogenicity of BMC grafts from two class I transgenic mice, D8 (B6 mice with an H-2Dd transgene) and C3H.Ld (C3H mice with an H-2Ld transgene). D8 BMC grafts are acutely rejected by B6 but not D8 recipients. This suggests that antigenic motifs associated with the H-2Dd molecule are recognized. B6 mice depleted of their CD3+ but not NK1.1+ cells can still reject D8 BMC grafts. These data suggest that NK1.1+/CD3- cells recognize the H-2Dd derived antigenic motifs. Similarly, C3H.Ld BMC grafts are rejected by B6 x C3H F1 but not B6 x C3H.Ld F1 recipients. Thus, antigenic motifs associated with the H-2Ld molecule can also be recognized. Furthermore, expression of either H-2Dd or H-2Ld by the recipients renders them unable to reject D8 or C3H.Ld BMC grafts. Therefore, H-2Dd and H-2Ld molecules appear to express common antigenic motifs recognized by NK cells. Additional studies with B6.R4 (KbIbSbDr), an intra-H-2 recombinant mouse, indicated that a third class I molecule, possibly H-2Dr, also shared the common antigenic motifs with both H-2Dd and H-2Ld molecules. Thus, positive recognition of class I antigens by NK cells can occur. However, expression of some of these antigenic motifs appear to be negatively controlled by certain H-2r genes as suggested by rejection of D8 and B6.R4 BMC grafts by D8 x B10.RIII F1 and B6.R4 x B10.RIII F1 hybrids respectively.

Animals↗

PubMed1993

The alpha 3 domain of the Qa-2 molecule is defective for CD8 binding and cytotoxic T lymphocyte activation.

Qa-2 is a nonclassical class I molecule encoded by the Q7 gene within the mouse major histocompatibility complex (MHC). Results from previous experiments on Qa-2, and on a chimeric Ld molecule (LQ3) in which the alpha 3 domain is encoded by Q7b, suggested that the alpha 3 domain of Qa-2 does not carry out the functions typical of the alpha 3 domains in other classical and nonclassical class I antigens. Class I molecules that contain the Qa-2 alpha 3 domain are poorly recognized by primary cytotoxic T lymphocytes (CTLs), and do not function normally in either positive or negative selection in vivo. By employing a cell-cell adhesion assay we demonstrate directly that the Qa-2 alpha 3 domain in the context of the LQ3 hybrid molecule cannot bind to human CD8, although other mouse class I alpha 3 domains bind efficiently. In addition, CD8-dependent CTL-mediated lysis of target cells, in a system which requires mouse CD8-class I alpha 3 domain interactions, is deficient in cells that express the Qa-2 alpha 3 domain. When combined with our earlier work on LQ3 transgenic mice, these results provide additional molecular support for the hypothesis that interaction with CD8 is required for both positive and negative selection of class I restricted T cells in the thymus. As the Qa-2 alpha 3 domain sequence does not differ from the previously defined minimal CD8 binding sequence of other class I molecules, these results also suggest that additional amino acids in the alpha 3 domain must be critical for CD8 binding and CTL activation.

Amino Acid Sequence↗

PubMed1993

Analysis of T cell receptors specific for recognition of class IB antigens.

T cells that recognize a peptide presented by a self-class IA molecule generally use a restricted repertoire of V beta and V alpha receptors. In contrast, alloreactive T cells, which recognize alloantigens that present a wide array of peptides, use a diverse repertoire, particularly in the CDR3 loop. Because the T cell repertoire directed against class IB alloantigens is not known, we examined V-D-J sequences in V beta chains specific for Qa-1 and similar sequences in both V beta and V alpha chains specific for Qa-2. We observed that 14 Qa-1-specific clones use a limited number of V beta segments and 8 of 14 express V beta 8.2 and have a conservation of charged residues in the CDR3 loop, particularly between residues 99 and 101. Thirteen of the 14 clones rearrange to the second J beta cluster and use within this cluster is restricted. Alloreactive anti-Qa-1 T cells can be assigned into three different specificity groups based on a Qa-1 modifying gene, Qdm, as well as Qa-1 epitope expression on Tap-2-deficient RMA-S cells. Receptors from members of each specificity group are more similar in their CDR3 loop to each other than members of the other groups. These data lend support to the Qa-1 class IB Ag presenting a limited number of peptides to T cells or in some manner limiting the development of a diverse alpha beta T cell repertoire. The alpha- and beta-chains from nine alloreactive anti-Qa-2 clones were analyzed. V beta use was limited to use of V beta 7 or a member of the V beta 8 family. Rearrangements were solely to the second J beta cluster. The use of V alpha and J alpha segments were diverse. Although conserved residues or motifs were observed in the CDR3 regions of both the beta- and alpha-chains, the extent of conservation was less than that for anti-Qa-1 receptors. Anti-Qa-2 T cells can be divided into two specificities, Q6 and Q7. No common features were apparent between these groups.

Amino Acid Sequence↗

PubMed1993

Effect of IGF-1 on placental prostanoid production.

Prostanoids play an important role throughout all of pregnancy and during the initiation and progress of labor. The human placenta, at term, produces large quantities of prostanoids, yet little is known of the steps regulating their biosynthesis. In these studies, the effect of IGF-I on the release of placental prostanoids was investigated. The basal release of prostaglandin E (PGE), prostaglandin F (PGF), thromboxane (TxB2) and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) increased from the fifth hour in culture, while the release of 13, 14-dihydro-15-keto-PGF2 alpha (PGFM) remained constant and hCG release decreased. The addition of IGF-I (10(-8) M) to the perfusing medium effected an inhibition of TxB2 and PGF within two and one-half hours of exposure. However, the release of PGE, PGFM, 6-keto-PGF1 alpha or hCG was not altered by IGF-I. Because both TxB2 and PGF are vaso-constrictors, we have proposed that IGF-I may enhance vasodilation in the placenta. Therefore, IGF-I may allow increased blood flow, thus affecting the maintenance of pregnancy and supply of nutrients for the growth of the fetus.

6-Ketoprostaglandin F1 alpha↗

PubMed1993

The effect of chronic graft-versus-host disease on B cell development.

Chronic graft-versus-host disease often results in a combined deficiency of humoral and cell-mediated immunity. Clinical and experimental studies have suggested that the decrease in B cell responsiveness is due to a failure of B cell production in the bone marrow, intrinsic B cell defects, excessive suppressor T cell activity, and deficient T helper activity. In the present study, we analyze the basis of B cell immunodeficiency in C.B-20-->(C.B-20 x B10.D2)F1 animals afflicted with chronic GVHD. The initial decline in B cell production in the BM accounts for the early reduction in the number of B cells in the spleen and BM. Later, as B cells appear in near-normal numbers in the BM, the spleen and lymph node are repopulated by the newly derived B cells. Associated with the appearance of B cells in the BM and spleen is the ability to respond to lipopolysaccharide. In contrast, both B cell populations are severely diminished in their ability to proliferate in response to agar-derived mitogens to form colonies (CFU-B). The reduction in the CFU-B response is most likely a consequence of an inherent B cell defect, since purification of C.B-20-->F1 splenic B cells does not restore the colony-forming potential. Unlike BM and splenic B cells, LN B cells are unable to respond to either mitogen. Taken together, these results imply that a population of B cells derived from a distinct lineage and/or B cell maturation is defective in mice undergoing GVHD.

Animals↗

PubMed1993

Effects of bone marrow-derived natural suppressor activity on B cell responses to lipopolysaccharide.

Natural suppressor (NS) activity is detected in tissues undergoing intense hematopoietic regeneration. This includes the spleens of mice recovering from total lymphoid irradiation or cyclophosphamide treatment, or after induction of chronic graft-versus-host disease against minor histocompatibility antigens. NS cells are thought to act via an antiproliferative mechanism, based on the observation that NS cells inhibit thymidine ([3H]TdR) uptake by mitogen- or antigen-activated lymphocytes. In the present study, the mechanism of B cell inhibition by NS activity present in normal adult bone marrow is analyzed. [3H]TdR uptake of LPS-stimulated B cells is inhibited by the presence of bone marrow cells (BMC). Consistent with the decrease in DNA synthesis, cell cycle analysis reveals that the majority of B cells fail to exit G0. To determine whether cells in G1 are also susceptible to inhibition by BMC, we tested the ability of cells with NS activity to inhibit the LPS response of either low-density B cells or B cells preactivated by LPS. Both populations of cells were readily inhibited in their uptake of [3H]TdR. Direct analysis of B cell growth in suppressed cultures demonstrates that B cell numbers remain constant, with only 6-30% of the control number of B cells present in cultures containing BMC. Taken together, these results indicate that the antiproliferative effect of NS cells is a result of not only resting B cells being inhibited from entering the cell cycle, but also the inhibition of B cells already in G1.

Animals↗

PubMed1992

T cell recognition of QA-1b antigens on cells lacking a functional Tap-2 transporter.

MHC class Ia H chains and beta 2-microglobulin assemble with appropriate peptides to form stable cell surface molecules that serve as targets for Ag-specific CTL. The structural similarities of class Ia and the less polymorphic Q/T/M (class Ib) molecules suggest that class Ib molecules also play a role in antigen presentation, although the origin of the peptides they present remains mostly unclear. The cell line RMA-S has a defect in class I Ag presentation, presumably due to a mutation in a peptide transporter gene. This defect can be overcome by transfection of RMA-S cells with the Tap-2 gene (formerly Ham-2) that encodes an ATP-binding transporter protein. We now show that a substantial portion of alloreactive CTL specific for Qa-1 class Ib molecules recognize Qa-1b on RMA-S cells and thus differ from most class Ia specific CTL. Those anti-Qa-1b CTL that do not recognize untransfected RMA-S do lyse RMA-S transfected with Tap-2. We also examine the effects of Qdm, a gene that maps to the D region and alters recognition of Qa-1. Qdm(k) strains lack an epitope(s) recognized by some (Qdm dependent) anti-Qa-1 CTL whereas Qdm+ strains express this epitope. Thus, Qdm-dependent CTL do not recognize Qa-1 on Qdm(k) targets whereas Qdm-independent CTL recognize Qa-1 epitopes in all strains. Although Qdm-independent CTL varied as to whether they recognized RMA-S vs RMA, all nine Qdm-dependent clones only recognized Qa-1b on RMA and not RMA-S. This result is consistent with Qdm encoding a peptide dependent upon the TAP transporter for cell membrane expression.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1992

Ham-2 corrects the class I antigen-processing defect in RMA-S cells.

The murine major histocompatibility complex (MHC) contains two genes (Ham-1 and Ham-2) that encode members of a super-family of ATP-dependent transport proteins. These genes are believed to mediate the transport of peptide antigen from the cytoplasm into the lumen of the endoplasmic reticulum for binding by MHC class I molecules. Evidence for such a function has come from the rescue of class I surface expression by a cloned copy of the human homologue of Ham-1, PSF-1, in a human cell line that is defective in antigen processing. A mutant murine cell line, RMA-S, has an identical antigen-processing-defective phenotype. Here we show that expression of a cloned copy of the Ham-2 gene in RMA-S cells results in recovery of the ability to process and present class I-restricted antigens to cytotoxic T lymphocytes, and in partial recovery of class I surface expression. Processing defects for classical (H-2 K and D) and non-classical (Qa1 and HMT) class I molecules are corrected by Ham-2. These data indicate that both MHC-linked transporter genes are probably required for class I antigen processing, and that the functional transporter in this pathway may consist of a Ham-1/Ham-2 heterodimer.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1991

Negative and positive selection of antigen-specific cytotoxic T lymphocytes affected by the alpha 3 domain of MHC I molecules.

The alpha 1 and alpha 2 domains of major histocompatibility complex (MHC) class I molecules function in the binding and presentation of foreign peptides to the T-cell antigen receptor and control both negative and positive selection of the T-cell repertoire. Although the alpha 3 domain of class I is not involved in peptide binding, it does interact with the T-cell accessory molecule, CD8. CD8 is important in the selection of T cells as anti-CD8 antibody injected into perinatal mice interferes with this process. We previously used a hybrid class I molecule with the alpha 1/alpha 2 domains from Ld and the alpha 3 domain from Q7b and showed that this molecule binds an Ld-restricted peptide but does not interact with CD8-dependent cytotoxic T lymphocytes. Expression of this molecule in transgenic mice fails to negatively select a subpopulation of anti-Ld cytotoxic T lymphocytes. In addition, positive selection of virus-specific Ld-restricted cytotoxic T lymphocytes does not occur. We conclude that besides the alpha 1/alpha 2 domains of class I, the alpha 3 domain plays an important part in both positive and negative selection of antigen-specific cells.

Animals↗

PubMed1991

Three-dimensional treatment planning considerations for prostate cancer.

Over 300 treatment plans for a total of eight disease sites based on 3-D treatment planning considerations utilizing serial CT delineated target volumes were generated by four institutions as part of an NCI supported contract to both assess the current state-of-the-art capabilities and point directions for future efforts. Two patients with stage C prostate cancer were evaluated with protocol plans which required treatment of the prostate to 70 Gy and the pelvic lymph nodes to 46 Gy. When full 3-D target definition and multiple beam arrangements were employed, all institutions were able to submit plans which scored higher on tumor coverage and had lower normal tissue complication scores compared to traditional plans. The 3-D plans using standard beam arrangements, however, were often rated as highly as the 3-D unconstrained plans due to the multiple beam arrangements already selected to optimize standard plans at most institutions. For this site, heterogeneity corrections, beam energy changes and changes in CT number did not substantially change plan scores.

Aged↗

PubMed1991

The Q7 alpha 3 domain alters T cell recognition of class I antigens.

In this study we have analyzed the role of the alpha 3 domain of class I molecules in T cell recognition. Using the laboratory engineered molecules LLQQ (alpha 1/alpha 2 from Ld, alpha 3, and phosphatidyl inositol (PI) linked C terminus from Q7) and LLQL (alpha 1/alpha 2 from Ld, alpha 3 from Q7, transmembrane (TM) and cytoplasmic domains from Ld) we show that these molecules are not recognized by primary Ld-specific CTL. The cell membrane expression of both Ld and LLQL are upregulated by co-culture with an exogenously supplied murine cytomegalovirus-derived peptide indicating that the Q7 alpha 3 domain does not interfere with binding of Ag to alpha 1/alpha 2. However, only peptide pulsed Ld but not LLQL target cells are recognized by Ld-restricted-peptide specific CTL. In contrast to the above results, LLQL and LLQQ molecules can be recognized by bulk alloreactive anti-Ld CTL and 2/3 of CTL clones derived from in vivo primed mice. The fact that these secondary CTL recognize LLQQ indicates that a PI linkage is permissive for presentation of class I epitopes to alloreactive CTL. These secondary CTL are resistant to blocking at the effector stage by mAb against CD8 and express relatively low levels of membrane CD8 molecules compared to CTL from unprimed mice. Further, culture of unprimed CTL precursors in the presence of CD8 mAb also allows for the generation of CD8-independent CTL that recognize LLQL. Taken together, these data indicate that the alpha 3 domain of Q7 (Qa-2) prevents CD8-dependent CTL from recognizing Ld, regardless of whether the class I molecule is attached to the cell surface by a PI moiety or as a membrane spanning protein domain. We hypothesize that this defect in recognition is most likely due to an inability of CD8 to interact efficiently with the Q7 alpha 3 domain and could account for why Q7 molecules do not serve as restricting elements for virus and minor H-Ag-specific CTL.

Animals↗

PubMed1991

Two roles for CD4 cells in the control of the generation of cytotoxic T lymphocytes.

The generation of CTL against Qa-1 Ag in C57BL/6 (B6) (Qa-1b) and B6.Tlaa (Qa-1a) congenic strains requires in vivo priming with the Qa-1 alloantigen together with a helper Ag, such as H-Y. The primed precursors obtained from these female mice generate Qa-1-specific CTL activity upon culture in vitro. Although the presence of the H-Y helper Ag is not required for the in vitro sensitization, no response occurs in the absence of CD4 cells. Addition of unprimed B6.Tlaa CD4 cells from Qa-1 incompatible radiation bone marrow chimeras (B6.Tlaa----B6), that are presumably tolerant to Qa-1b, provide helper activity for Qa-1b-specific CTL. This indicates that although CD4 cells are obligatory for the Qa-1 response, they need not be specific for alloantigens on the APC to generate helper activity in in vitro cultures. Addition of unirradiated B6 CD8-depleted spleen cells to CD4-depleted B6.Tlaa anti-B6 cultures in the presence of either B6.Tlaa CD4 cells or rIL-2 prevents the generation of Qa-1 specific CTL. This inhibition is not due to an anti-idiotypic Ts cell since B6.Tlaa----B6 chimeric cells do not suppress an anti-Qa-1b response. Rather, this finding is consistent with that of a veto cell mechanism. To determine whether CD4 cells themselves exhibit veto activity, highly purified CD4 populations were tested for their ability to inhibit the generation of Qa-1-specific CTL. CD4 cells precultured for 2 to 3 days with Con A and rIL-2 specifically inhibit CTL activity whereas resting cells do not, similar to that noted for CD8 veto cells. The relative efficiency of activated CD4 cells is greater than that of resting NK cells but is less than that of activated CD8 or NK cells. Thus, CD4 cells not only provide helper activity for CTL precursors, but also act as veto cells to prevent the generation of CTL activity.

Animals↗

PubMed1991

Dose-related action of gonadotropin-releasing hormone on basal prostanoid production from the human term placenta.

The dose-related effect of gonadotropin-releasing hormone on placental prostanoids was studied with a perifusion system. Villous tissues were perifused with medium 199 (1 ml/hr) and at the beginning of the fifth hour, either 0, 10(-10), 10(-9), 10(-8), 10(-7), or 10(-6) mol/L gonadotropin-releasing hormone was added to the medium of triplicate chambers. The concentration of prostaglandin E, prostaglandin F, 13,14-dihydro-15-keto-prostaglandin F2 alpha, 6-keto-prostaglandin F1 alpha, and thromboxane B2 in the effluent medium, collected every hour, was determined by specific radioimmunoassay. The cumulative release after gonadotropin-releasing hormone treatment for each chamber was calculated, and replicate chambers were averaged. Linear regression analysis of the average for each dose from three different placentas was used to determine the dose-response relationship. Gonadotropin-releasing hormone significantly inhibited the release of placental prostaglandin E, prostaglandin F, and thromboxane B2 in a dose-dependent fashion. Gonadotropin-releasing hormone had no significant effect on 13,14-dihydro-15-keto-prostaglandin F2 alpha and 6-keto-prostaglandin F1 alpha, although there was an apparent increase in 13,14-dihydro-15-keto-prostaglandin F2 alpha. These data support the hypothesis that chorionic gonadotropin-releasing hormone inhibits prostanoid production from the placenta, which in turn may regulate various functions of prostanoids during pregnancy.

6-Ketoprostaglandin F1 alpha↗

PubMed1991

Tolerance to liver-specific antigens.

We have described a TG model for peripheral tolerance of alloreactive CTL. Expression of Q10/L on hepatocytes renders mice functionally tolerant, although in vitro we observe that TG animals have normal numbers of CTL.Pf directed against this antigen. The basis for the tolerance presumably resides in the fact that the TG mice are lacking a subpopulation, either through deletion or anergy, that is responsible for recognition of the antigen on hepatocytes in vivo. The data are consistent with a tolerance model where cells with high affinity receptors are silenced. The presumed low affinity antigen-specific cells remaining in TG mice cannot be primed in vivo when immunized with antigen on spleen cells. Further, these CTL generate poor lytic activity in vitro. This failure to prime TG CTL in vivo could be attributed to primed cells traveling to the liver where they become tolerized when exposed to antigen on hepatocytes. However, we show that TG cells, after transfer to non-TG recipients, cannot be primed in vivo, indicating that the presumed low-affinity cells remaining in TG mice are not readily activable in this milieu. These data also indicate that this tolerance is not readily reversible during a 10- to 17-d time interval.

Animals↗

PubMed1990

Regulation of the cytotoxic T lymphocyte response against Qa-1 alloantigens.

Spleen cells from B6.Tlaa (Qa-1a) mice primed against C57BL/6 (Qa-1b) splenocytes in vivo generate Qa-1-specific CTL when rechallenged with Qa-1b Ag in vitro. The addition of unirradiated Qa-1b splenocytes to these cultures inhibits the generation of Qa-1-specific CTL. By using highly purified cell populations, we demonstrate that the only cell population in resting spleen capable of causing this inhibition is NK1.1+. Although resting CD8 cells lack inhibitory activity, purified CD8 cells precultured with Con A and IL-2 inhibit anti-Qa-1 CTL. This inhibition is specific for the Qa-1b Ag expressed on the inhibitor cells, is not due to cold target competition, and is thus similar to that ascribed to veto cells. Although NK cells from resting spleen inhibit the generation of Qa-1-specific CTL, NK cells precultured in the presence of Con A and IL-2 show an approximate 30-fold increase in veto activity. Thus, NK cells represent the most likely cell population for down-regulating anti-self class I-reactive CTL.

Animals↗