Biochemical documentation of allelic variation of the I-E antigens of the d, k, p, r, and u haplotypes

Mixed haplotypes and autoimmunity

Why do (NZB x NZW)F1 mice develop an autoimmune lupus-like syndrome? The second exons of the class II genes of NZB and NZW are identical to their counterparts of H-2d and H-2u haplotypes. Several lines of evidence suggest that this allows the production of a mixed haplotype molecule, I-E alpha dE beta z, and that this molecule plays a key role in the development of autoimmunity.

In vivo expression and function of hybrid Ia dimers (E alpha A beta) in recombinant and transgenic mice

We have found cell surface expression of an E alpha molecule in recombinant and transgenic mouse strains lacking an E beta molecule. Flow cytometry has shown low level expression of E alpha in B10.RQB3 (I-AqEk alpha) and B10.RFB2 (I-AfEk alpha) mice. We have also found that B10.Q (H-2q) mice can express the Ek alpha transgene. Since these strains do not have functional E beta chains, we propose that the E alpha A beta hybrid dimers are formed in low numbers and can be picked up by FACS analysis. So far we have not been able to identify these hybrid molecules by cytotoxicity or immunoprecipitation. The E alpha/A beta molecule can function in vivo during thymic selection in the clonal deletion of two V beta TCR subsets, V beta 11 and V beta 6, which have been shown to interact with the intact I-E molecule.

Alloreactivity of an OVA-specific T-cell clone. I. Stimulation by class II MHC and novel non-MHC B-cell determinants

A T-cell clone (Ly1-03) derived from BALB/cBy mice, though highly specific for OVA/Ad, reacted to allogeneic spleen cells of 6 of 12 H-2 haplotypes tested. The reactivity to each particular H-2 haplotype required the expression of a non-major histocompatibility complex (MHC) gene product present on the B cells of certain strains of mice. All the alloreactive responses were MHC restricted and were inhibited by class II-specific and L3T4-specific monoclonal antibodies. The non-MHC gene product, X, is a new lymphocyte-stimulating determinant that is not expressed in mice with the xid defect. We favor a model that proposes two independent sites (or receptors) for X and the class II molecule. Contrary to previous models for alloreactivity, the anti-MHC site is not directed to a polymorphic receptor for self-class II epitope on the foreign class II molecule, but rather to a conserved determinant present on both self- and allo-class II molecules. If there is only one antigen receptor on the T-cell clone Ly1-03, then anti-X receptor must bind to a cross-reactive determinant found on immunogenic OVA and the non-MHC coded gene product expressed on the cell surface membrane. We further postulate that class II plus "X" recognition may be a general rule for alloreactive as well as autoreactive responses. Thus, both allo-class II and allo-class I reactive T cells are similar in that both bind a non-MHC coded gene product prior to activation.

The expression of I-Ed molecules in F1 hybrid mice detected with antigen-specific, I-Ed-restricted cloned T-cell lines

The expression of polymorphic determinants on I-E molecules is largely dependent on allelic variation in the E beta chain. We have previously analyzed the expression of Ek beta and Eb beta chains in F1 hybrid mice by a combination of techniques, and have shown that functional variation detected by the responsiveness of cloned T-cell lines specific for these molecules correlates well with serological determination of E beta expression. In the present study, we have extended our analysis to Ed beta expression in F1 hybrid mice. We show that Ed beta is relatively poorly expressed in three F1 combinations: H-2d X H-2b, H-2d X H-2s, and H-2d X H-2u. The former two crosses express E alpha chains from the H-2d parent only; when recombinant strains carrying Eb beta or Es beta and an active E alpha gene are used, Ed beta expression is significantly increased. On the other hand, H-2u mice synthesize E alpha chains; the poor expression of Ed beta chains in this F1 hybrid apparently reflects the strong preferential association of Eu beta chains with all E alpha molecules thus far analyzed. These results confirm that E beta chains compete for binding to E alpha chains and that preferential association of different allelic forms of E beta chains with E alpha chains is a generalized phenomenon. They also illustrate the importance of the rate of biosynthesis of Ia chains for cell-surface expression.