Involvement of multiple factors in the clonal deletion of self-reactive T cells.

Self-tolerance is primarily induced by the elimination of potentially self-reactive T cells during early development of the T cell repertoire. In the mouse, endogenous mouse mammary tumor viruses (MMTV), including minor lymphocyte-stimulating antigens and milk-transmitted exogenous MMTV, have been known to function as self-antigens inducing the clonal deletion of self-reactive T cells in a V beta-specific manner. We investigated the factors involved in the deletion of V beta 17a-bearing T cells. The results indicated that in addition to the previously reported V beta 17a deletion ligand, Mtv-3, there is a nonmilkborne gene product which progressively deletes V beta 17a (and V beta 3)-bearing T cells during aging. This suggests that clonal deletion is mediated by multiple factors and that a clonal deletion element associated with aging may play a significant role in shaping the T cell repertoire.

Characterization of the Mlsf system. II. Identification of mouse mammary tumor virus proviruses involved in the clonal deletion of self-Mlsf-reactive T cells.

The genetic linkage of loci encoding stimulatory Mlsa and Mlsc determinants with proviruses of mouse mammary tumour viruses (MMTV) has been shown. We previously have reported that the ligand(s) for V beta 5, V beta 11, and V beta 12 behaves as a novel minor lymphocyte-stimulating (Mls) determinant(s), Mlsf, to induce the strong proliferation of unprimed T cells, and that this ligand(s) also functions as a self-Ag for the clonal deletion of self-reactive T cells. In the accompanying paper (Part I), a unique polymorphism characteristic of the Mlsf gene product is presented. In order to determine the genetic basis for this novel Mls system, we examined the progeny of multiple genetic crosses to identify the MMTV proviral loci involved in the clonal deletion of self-Mlsf-reactive T cells. Results from these investigations indicated that at least three known MMTV proviruses, Mtv-8, Mtv-9, and Mtv-11 are involved in the expression of Mlsf gene products. Presence of Mtv-9 results in the complete deletion of V beta 5, V beta 11, and V beta 12; Mtv-8 is associated with the complete deletion of V beta 12, but only a partial deletion of V beta 11 (primarily CD4-positive T cell subset) with little or no deletion of V beta 5; and Mtv-11 induces the complete deletion of V beta 11 and V beta 12, but no deletion of V beta 5. Given the significant sequence homology in the C-terminal portion of the open reading frame (ORF) region among these three MMTV and the almost equivalent effect of these three MMTV provirus upon the V beta 12 repertoire, their apparent hierarchic effect upon the V beta 5 and V beta 11 repertoires suggests that affinity differences in recognition of the same determinant by different TCR V beta may play a significant role in the clonal deletion of self-reactive T cells.

Characterization of the Mlsf system. I. A novel "polymorphism" of endogenous superantigens.

In addition to Mlsa (Mls-1a) and Mlsc (Mls-2a, Mls-3a), we and others have recently described a third set of stimulatory minor lymphocyte stimulating (Mls) determinants, which are ligands for "I-E related" V beta, V beta 5, V beta 11, and V beta 12. Although all V beta associated with the recognition of the conventional Mls determinants are, in general, uniformly deleted in those animals expressing relevant Mls, expression of Mlsf-related V beta reveals various deletion patterns among different strains. Here we describe extensive genetic studies to evaluate the relationship among the self-Ag responsible for clonal deletion of T cells bearing Mlsf-related V beta by using antibodies specific for TCR V beta chain. In addition, a panel of T cell clones specific for the Mlsf determinant were generated and employed to analyze the determinant specificity, which is recognized by Mlsf-reactive T cells in vitro as well as the role of class II molecules in T cell recognition of the Mlsf determinants. The results of these two independent approaches provide evidence that the Mlsf system is composed of a set of gene products that reveal a unique polymorphism in the induction of clonal deletion in vivo and in T cell activation in vitro. One of these gene products causes almost complete deletion of the self-Mlsf reactive T cell repertoire in vivo and elicits a strong proliferative response to Mlsf-specific T cell clones. Expression of the other gene products results in the clonal deletion of only part of the Mlsf-reactive T cell repertoire. Furthermore, the response pattern of Mlsf-specific clones to intra-MHC recombinant inbred strains and the inhibition pattern of these clones by anti-class II antibody suggested that although expression of the I-E molecule is essential for T cell recognition of Mlsf determinants, the A beta gene may also contribute to the efficient presentation of Mlsf determinants by forming unique class II E alpha A beta molecules.

Characterization of a new minor lymphocyte stimulatory system. I. Cluster of self antigens recognized by "I-E-reactive" V beta s, V beta 5, V beta 11, and V beta 12 T cell receptors for antigen.

In the mouse, two sets of V beta gene products have been shown to be associated with T cell recognition of endogenous self Ag. One of these is the set of V beta associated with T cell reactivities to stimulatory Mls gene products, Mlsa (V beta 6, V beta 8.1, V beta 9) or Mlsc (V beta 3); another is the set of V beta, such as V beta 5, V beta 11, V beta 12, or V beta 17a, which were originally found to be related to I-E recognition. Although the Mls system has been well characterized, little is known about the nature of the ligands for the second set of V beta. In this work, we describe the evidence that the natural ligand or ligands of V beta 5, V beta 11, and V beta 12 may be novel Mls determinants that are recognized by naive T cells at a high precursor frequency and function as the ligand for clonal deletion of self-reactive T cells by negative selection. However, surprisingly, unlike the conventional Mls system, in which all V beta associated with Mlsa recognition or Mlsc recognition are uniformly deleted in those animals expressing the relevant Mls type, expression of these three V beta segregates independently among strains. Based on these observations, the nature of T cell recognition for this new Mls gene product(s) is discussed.

Genetic analysis of the Mls system. Formal Mls typing of the commonly used inbred strains.

In order to elucidate the biological role of minor lymphocyte stimulating (Mls) gene products, we have been investigating the fundamental immunogenetic characteristics of the Mls system. In this report, we describe the distribution of stimulatory Mls products, Mlsa and Mlsc, in a panel of laboratory inbred strains based on the response pattern of H-2-compatible naive T-cell populations as well as monospecific Mlsa- or Mlsc-reactive T-cell clones. In addition, the expression of four different T-cell receptor (Tcr) b-V segment Tcrb-V3, -V6, -V8.1, and -V9, which were recently reported to be associated with T-cell recognition of Mls gene products in these strains, was examined. The results indicate that the majority of commonly used laboratory strains including those originally typed as Mlsa are also expressing Mlsc determinants and that very few independent inbred strains are non-Mlsc. Moreover, the pattern of Tcrb-V expression in spleen as well as in thymus suggests that the association between Mls expression and clonal deletion of self Mls-reactive T cells appears to be the general rule in inbred strains. Based on these results, implications for the nondetectable Mls-like gene products in other species besides the mouse are discussed.

Analysis of Mlsc genetics. A novel instance of genetic redundancy.

The identity of the self determinants involved in the selection of the T cell repertoire has been a matter of considerable interest. In addition to the apparent critical role of MHC gene products, accumulated experimental results indicate the importance of non-MHC gene products in T cell repertoire selection. In particular, murine Mlsa and Mlsc determinants have been shown to be highly stimulatory to allogeneic T cells and to be involved in the negative selection (elimination) of self-reactive T cells expressing selected TCR V beta segments. In this work, a unique phenomenon of genetic redundancy is described in the control of Mlsc expression: Mlsc appears to be controlled by at least two unlinked loci, and the product of either one of these loci is sufficient to evoke Mlsc-specific T cell response and to act as a ligand in the deletion of self Mlsc-reactive V beta 3+ T cells. Based on these findings, we propose a possible explanation for the fact that Mls-like genes or gene products have not been identified in other species such as man.