Marek B. Zaleski

Genetic Control of the Immune Response to Thy‐1 Antigens1

CONTENTS

Gene(S) at I-A Subregion Controls the Autoimmune Response to Thyroglobulin in Mice

Immunization of mice with thyroglobulin emulsified in Freunds complete adjuvant produces autoimmune thyroiditis, characterized by antibodies to thyroglobulin and infiltration of the thyroid with mononuclear cells. Some strains of mice are low and others are high responders to thyroglobulin. The immune response as reflected especially in the magnitude of the thyroid infiltration, is controlled by gene(s) within the H-2 locus. Previous attempts to map the Ir gene(s) for thyroglobulin (Ir-Tg) showed that it could be assigned to either the K or I-A subregion of H-2. An H-2 recombinant strain of mice, B10.MBR (H-2bq1), in which the H-2K is derived from the H-2b haplotype and which carries the I-Ak allele(s), was immunized with thyroglobulin. B10.MBR mice were high responders to thyroglobulin in contrast to C57BL/6 mice, which have both the H-2K and I-A from the H-2b haplotype and were low responders. This suggests that Ir-Tg, which controls the severity of autoimmune thyroiditis, maps within the I-A subregion, similar to gene(s) controlling the susceptibility to experimental myasthenia gravis.

Effect ofH-2 incompatibility between recipient and donor on the magnitude of response to Thy-1.1 antigen

Mice were immunized intravenously with 4 × 107 thymocytes from Thy-1 disparate, eitherH-2-compatible orH- 2-incompatible donors. The magnitude of the anti-Thy-1.1 response was measured by determining the number of PFC in spleens of animals 6 days after immunization. Regardless of the origin of immunizing and target thymocytes, the assay employed detected exclusively PFC-producing antibodies to the Thy-1.1 antigen. In almost all instances,H-2-compatible thymocytes elicited a significantly higher response than didH-2-incompatible thymocytes, although the latter occasionally evoked a high response. TheH-2 incompatibility between donor and recipient appeared to be responsible for the differences in responsiveness of the standard inbred mice and theirH-2 mutants immunized with thymocytes compatible with standard inbred strains. The phenomenon observed appears to have several features in common with antigenic competition. We propose that the requirement forH-2 compatibility in the anti-Thy-1.1 response may be the expression of a general requirement of T cells to recognize an antigen in the context of the H-2 molecule.

Preliminary Analysis of Primary and Secondary Anti-Thy-1 Responses Elicited by Immunization with Cell-Bound and Cell-Free Antigen

Primary and secondary anti-Thy-1 responses were elicited in C57BL/6Kh and (C57BL/6Kh X BALB/cKh)F1 mice by injection of either intact or sonicated Thy-1 disparate thymocytes as the source of the two forms of Thy-1 antigen--cell bound and cell free, respectively. The primary response was characterized by a high number of anti-Thy-1 plaque-forming cells in the spleen and a high titer of serum antibodies that belonged predominantly to the IgM class. The secondary response consisted of a moderate number of plaque-forming cells and a high titer of serum antibodies that belonged to the IgG and IgM classes. Only secondary responses ensued in mice primed and boosted with the same form of antigen, whereas primary and secondary responses developed concomitantly in animals primed with one form and boosted with both forms simultaneously. These data suggested that the two forms of Thy-1 antigen activate in a given responder two discrete subsets of T cells.

Non-H-2 Antigens Serving as Carrier Determinants in a Primary Anti-Thy-1 Response in Mice

The primary immune response of mice to the Thy-1 antigens was elicited by intravenous injection of thymocytes from H-2 compatible donors. The magnitude of the ensuing response judged by the number of plaque forming cells producing antibodies lytic for the Thy-1 bearing cells was influenced by some non-H-2 antigens present on the immunizing thymocytes. Absence of non-H-2 incompatibility resulted in a poor response whereas the presence of such an incompatibility allowed a good response. Genetic analysis revealed that the non-H-2 incompatibility affecting the anti-Thy-1 response is controlled by 1-3 independently segregating genes presumably determing molecules acting as carrier determinants for otherwise poorly immunogenic Thy-1 antigens. The carrier effect appeared to be influenced by the gene dosage of the carrier molecules on the immunizing cells. The data presented are discussed in the context of the current concepts of the mechanisms controlling various immune responses.

The search for h-2 complementation affecting the anti-thy-1 response in mice: a progress report.

It has been postulated that combinatorial Ia molecules of IAb/Iad heterozygotes are involved in the recognition of the Thy-1 alloantigens. These molecules could be considered the products of the complementary Ir-Thy-1 genes. In present studies, no complementation was found among 37 different H-2 heterozygous F1 hybrids except those carrying IAb/IAd haplotypes. However, in two instances involving hybrids carrying IAr alleles anti-Thy-1 responses were found to be better than expected. The possible mechanism(s) of such responses is currently under investigation.

Retrovirus-induced Lymphoproliferative Disease in Mice Undergoing Graft-versus-host Reaction

The effect of graft-versus-host reaction on the course of concommitant retrovirus-induced lymphoproliferative disease was investigated. The graft-versus-host reaction was elicited by a single i.v. injection of 1.2 x 10(8) parental spleen cells into adult F1 mice. Lymphoproliferative disease was induced by a single transfusion of 0.2 ml of whole blood from donors with fully developed disease, induced by infection with retrovirus LP-BM5 MuLV. Graft-versus-host reaction and the lymphoproliferative disease each separately produced similar syndrome consisting of splenomegaly, lymphadenopathy, leukopenia, neutrophilia, reduced in vitro proliferation of spleen cells and suppression of in vivo immune responsiveness. The above symptoms were usually less pronounced during graft-versus-host reaction. Ongoing graft-versus-host reaction neither aggravated nor accelerated the course of the virus-induced lymphoproliferative disease in genetically susceptible F1 hybrids. Likewise, an ongoing graft-versus-host reaction in genetically resistant F1 hybrids did not alter their susceptibility to the retrovirus infection. The apparent lack of the effect of graft-versus-host reaction -dependent immunosuppression on the severity and the course of the concommitant retrovirus-induced lymphoproliferative disease suggests pathogenic differences between the murine syndrome and human AIDS for which the murine disease is considered by some to be an animal model.

Macrophage IA Hybrid Molecule as Product of the Ir-Thy-1 Genes

A primary anti-Thy-1 response in mice is under complex genetic control (Zaleski et al. 1986). This control has been shown to involve either class I or class II H-2 molecules depending on the form in which the Thy-1 antigen is presented to a responder. Briefly, when thymocytes from an H-2-compatible donor are used, the cell-bound Thy-1 antigen seems to be presented directly to the responder’s T cells. The latter are believed to require simultaneous stimulation by the carrier-like or helper determinants (Lake and Douglas 1978) or acolytes (Klein and Zaleski 1987). In contrast, when thymocytes from H-2-incompatible donors are used, the cell-free Thy-1 antigen, which is shed from the immunizing thymocytes, appears to be presented by the responder’s macrophages. This presentation most likely involves associative recognition of the Thy-1 antigen and the product of the two complementary Ir-Thy-1 genes (Zaleski and Klein 1978). Recently, it was demonstrated that the product of these genes is identical with a hybrid IA molecule (Quackenbush et al. 1985, Zaleski et al. 1985). The working hypothesis outlined above is based on two crucial observations. First, a good anti-Thy-1 response to the cell-free antigen is demonstrable only in F1 hybrids that express a particular hybrid IA molecule (Quackenbush et al. 1985). Second, in vivo administration of monoclonal antibodies specific for a particular class II molecule inhibits the response to the cell-free, but not to the cell-bound antigen (Zaleski et al. 1985, Quackenbush et al. 1987).

MAPPING THE Ir-Thy-1 LOCUS TO THE K REGION OF THE H-2 COMPLEX

The primary immune responses of H-2 recombinant and H-2 mutant mice to the Thy-1.1 antigen were compared with the responses of the corresponding parental strains. In both instances, the magnitude of the responses, as measured by the number of PFC/spleen, was associated with alleles at the K rather than the I region of the H-2 complex. To explain these findings, a working hypothesis has been advanced that one of the Ir-Thy-1 loci involved in the control of the responsiveness to the Thy-1.1 antigen may be in the K region or even identical to the H-2K locus.