David, Chella S.

Abstract MLR suppressor factor (MLR-SF) optimally suppresses MLR responses only of responder cells which are compatible in the I-C subregion with cells producing the factor. Therefore, presence of MHC-encoded determinants on MLR-SF has been investigated, with particular interest in I-C, as well as the possible role of I-J determinants. Suppressor activity of supernates of alloantigen-activated spleen cells was tested after passage over solid immunoadsorbants prepared with various anti-H-2 subregion sera. Immunoadsorbants with specificity towards K and D region products were ineffective while several preparations with I region specificity removed suppressor activity from factors of the appropriate haplotype. The single subregion specificity common to all adsorbing preparations was I-C. Recently, ambiguity has developed with regard to genetic resolution of I-C and adjacent subregions, including difficulties of serologic differentiation of I-C products of the k and d haplotypes. Antisera prepared in I-Ck/I-Cd disparate strain combinations have identified T cell restricted determinants which are distinct between these haplotypes. MLR-SF prepared from (BALB × CBA)F1 were passed over I-Cd and I-Ck specific adsorbants and residual activity tested in MLR with each parental responder cell. Exposure to anti-I-Cd removed suppressor activity for the BALB response, leaving intact suppression of CBA responses. The reciprocal situation also obtained. Furthermore, acid elution of anti-I-Cd columns exposed to F1 factor yielded material which suppressed BALB but not CBA MLR. Antisera with anti-I-Jk specificity did not remove suppressor activity of various H-2k factors. In addition, control factors passed over anti-I-Jk columns did not acquire suppressive activity, indicating that leaching of small quantities of anti-I-J antibodies had not concealed actual binding of suppressor molecules, by inducing a distinct form of suppression. Thus, I-C subregion products, restricted to T lymphocyte expression, exhibit unique association with MLR-SF suppression of MHC stimulated immune responses.

Abstract Analysis of the tryptic peptides obtained from the Ia.7-positive, "I-E" antigens produced by 4 F1 combinations derived from strain A.TFR5 has provided biochemical confirmation that I-A/I-E gene complementation can occur in the trans configuration. The data obtained support the concept that structural genes, as opposed to regulatory genes, are the essential elements involved in this complementation and support the assignment of the I-E subregion of strain A.TFR5 as I-Ek. The data support the following assignments of the genes encoding the E beta chains: B10.A(4R) as E beta k, B10.A(5R) as E beta b, and B10.HTT as E beta s. Finally, data are presented demonstrating that the E beta chain derived from the recombinant D2.GD strain partially differs from the E beta d chain derived from a conventional H-2d haplotype strain, B10.D2.

Abstract When MHC congenic and recombinant mice are inoculated with Torpedo acetylcholine receptors (AChR) with adjuvants, the magnitude of autoantibody responses to muscle AChR and the defect of neuromuscular transmission closely parallel in vitro lymphocyte proliferative responses to Torpedo AChR. All of these responses are controlled by gene(s) at the I-A subregion of the H-2 complex. Data presented in this report confirm in back-cross mice that T lymphocyte proliferative responses to AChR are controlled by a Mendelian dominant gene linked to H-2, at the I-A subregion. Lymphocyte responses were eliminated by blocking Ia antigens on lymph node cell surfaces with appropriate anti-I-A alloantisera and by removal of adherent cells. A spontaneous mutation at the I-A subregion in the B6 strain, which resulted in structural alteration of the A beta chain of Ia, converted high responsiveness to AChR to a state of low responsiveness. These data implicate a macrophage-associated Ia molecule in induction of autoimmune responses to AchR, probably in the presentation of AChR to helper T lymphocytes that thereby help B lymphocytes to differentiate into anti-AChR antibody-forming cells.

Abstract The proliferative response of regional lymph node lymphocytes to Torpedo acetylcholine receptor (TAR) is under H-2 linked Ir gene control. In high responder B6 (H-2b) congenic mice, lymphocytes that proliferate in vitro in response to TAR are dependent on T cells of a subpopulation expressing the phenotype associated with helper functions, Lyt-1+23-.

Abstract The genetic control of T lymphocyte proliferative response to the five synthetic antigenic sites of myoglobin, two synthetic nonantigenic control peptides, and one “nonsense” peptide was determined in independent and recombinant strains of mice. In all the strains examined, the nonantigenic control peptides and the “nonsense” peptide did not invoke a response in myoglobin-primed mice. Further, when mice were not primed with whole myoglobin, no response was obtained with any of the antigenic sites. Haplotypes H-2d, H-2f, and H-2s are higher responders to sites 1 and 2, whereas haplotypes H-2d and H-2s are high responders to site 5. Response to site 3 may be controlled by a non-H-2-linked gene. Site 4 can stimulate H-2b and H-2k haplotypes that are nonresponders to the whole myoglobin. Studies with the recombinant strains suggested that Ir genes to sites 1 and 2 map in the I-A subregion and I-C subregion and were designated Ir-Mb-1,2(A) and Ir-Mb-1,2(C). Ir genes to sites 4 and 5 mapped only in the I-A subregion and were designated Ir-Mb-4(A) and Ir-Mb-5(A). These studies suggest that individual antigenic sites in a molecule are controlled by unique Ir genes.

Abstract The I-E molecule is produced by complementation of genes in I-A (Ae) and I-E (E alpha). Ia specificities 22 and 23 are generated by the hybrid molecule, whereas Ia.7 is an allotypic determinant presumably on the alpha-chain of the I-E molecule. Recombinant A.TFR5 (AfEk) lacks detectable I-E molecule since Af and Ek cannot complement. In a cross between A.TFR5 and B10.A(4R) (AkEb), Aek and E alpha k can successfully complement to express the I-Ek molecule on the cell surface of the heterozygote. Haplotypes H-2b and H-2s can also provide the permissive Abe and Ase molecules for complementation with Ek alpha of A.TFR5.

Abstract Studies on the genetic control of immune response to sperm whale myoglobin were initiated. As demonstrated in this paper, the T lymphocyte proliferative response to whale myoglobin is under H-2-linked Ir gene control. Mice of H-2d, H-2f, and H-2s haplotypes were high responders to the myoglobin, whereas haplotypes H-2b, H-2k, H-2p, H-2q, and H-2r were low responders. The Ir gene(s) was localized between H-2K and H2D regions, since the recombinant strain A.TL (KsIkSkDd) was a low responder and A.TH (KsIsSsDd) was a high responder. Further studies with recombinant strains revealed that the expression of the high-responder I-Ad or I-As alleles was sufficient to give a good response, since strains D2.GD (d d b b b b b b) and B10.HTT (s s s s k k k d) were high responders. The expression of the I-Cd allele in strains B10.A (k k k k k d d d) and B10.A(5R) (b b b k k d d d) also gave high response, and thus suggested a second Ir gene, derived from the H-2d haplotype. The finding that expression of the I-Cs allele in B10.S(8R) (k k ? ? s s s s) did not result in high response suggests the lack of the second Ir gene in the high-responder H-2s haplotype.

Abstract MS is an autoimmune disease of the CNS and among all the genetic factors; MHC class-II molecules show the strongest association. To better understand the role of MHC class-II (HLA-DR/DQ) genes in susceptibility and resistance to MS, we utilized transgenic (Tg) mice expressing HLA class-II gene lacking endogenous mouse class II genes. HLA-DR3 Tg mice are susceptible to PLP91-110 induced experimental autoimmune encephalomyelitis (EAE), whereas DQ8 (DQB1*0302) transgenic mice are resistant. To identify the gene expression changes and pathways required for disease susceptibility vs resistance to EAE, we performed mRNA expression profiling of CD4+ T cells from HLA-DR3 (susceptible) and HLA-DQ8 (resistant) Tg mice. Whole genome expression analysis identified 2945 genes in HLA-DR3 Tg mice (PLP91-110 immunized vs. naïve) and 1053 genes in HLA-DQ8 Tg mice (PLP91-110 immunized vs. naïve). Comparison of modulated genes between DR3 and DQ8 identified 772 genes common to both strains, 2173 genes unique to DR3 whereas 281 genes were unique to DQ8 mice. Ingenuity pathway analysis showed up regulation of pathways involved in T cell signaling in inflammation, NF-kB signaling and those responsible for communication between innate and adoptive immunity. Majority of these pathways have IL1β as a major upstream regulator in disease susceptible HLA-DR3 Tg mice. Thus microarray data indicates an important role of IL1β induced encephalitogenic T helper cell differentiation in disease susceptibility.

MHC Class II molecules are essential in antigen presentation and selection of the CD4+ T cell repertoire. They are mainly expressed on professional Antigen Presenting Cells (APC), i.e. B lymphocytes, dendritic cells and macrophages. Activated human T lymphocytes also express MHC Class II but MHC Class II expression is not detected on activated mouse T cells. HLA‐DR3 can be expressed as a transgene on CD4+ T cells in complete MHC Class II knock‐out (AEo) mice, but not in I‐Ab knock‐out (Abo) mice, suggesting that a gene, which could modify the expression of HLA‐DR3, might exist between I‐A and I‐E. Expression sequence tag (EST) databases were searched using the flank regions between I‐A and I‐E and a new potential gene was identified. No similar sequence was found in the human genome database. Expression in multiple mouse tissues, but not in human cell lines, was verified by RT‐PCR. However, this gene was found to be expressed in B6 mouse B cells and two mouse B cell lines, but not in T cells, indicating that it might not be related to the expression of HLA‐DR3. Transduction of this gene into the LG2 cell line had no effect on MHC II expression. In summary, we report the discovery of a new gene between the I‐Aa and I‐Eb1 region in C57BL/6 mice and its function remains unknown. (Supported by NIH‐AI30554)

To understand the role of regulatory T cells in staphylococcal enterotoxin B‐induced toxic shock syndrome (TSS), we performed gene expression profiling in HLA‐DR3 transgenic mice using microarrays. We observed that at 3 hours after systemic exposure to SEB (10 μg), the splenic expression of FoxP3, a hall mark of regulatory T cells, was increased by 5 folds (p<0.005). In addition, other genes that regulate FoxP3 + Tregs were also significantly modulated by SEB. These include IL‐2R (27‐fold), IL‐2 (234‐fold), IL‐6 (689‐fold), IL‐21 (21‐fold), TGF‐B1 (0.7‐fold), IL‐17 (5.5‐fold) and IL‐22 (98‐fold). To further characterize the homeostasis of Tregs cells during superantigen‐induced TSS in vivo, HLA‐DR3 transgenic mice were first challenged with SEB and were administered BrdU in drinking water for 3 days. Mice were killed 3 days later and splenocytes analyzed by flow cytometry. We observed that in addition to FoxP3‐TCR Vβ8 + T cells, FoxP3 + TCR Vβ8 + T cells also significantly expanded in vivo as evident from their BrdU staining patterns. This indicated that SEB is able to activate Tregs as well. Depletion of Tregs using anti‐CD25 antibodies (clone PC‐61, 500 ug/mouse) 2 days prior to SEB challenge did not significantly alter serum cytokine levels as compared to control mice treated with rat IgG and SEB. Thus, T regulatory cells have a minimal role in SEB‐induced TSS.