Demyelinating autoimmunity: murine T cell epitopes of MBP and primate T cell receptor Vβ variation
Autoimmune diseases result from inappropriate self-reactivity by lymphocytes. The long-term goal is to generate specific therapies for autoimmune diseases of humans, the success of which hinges on the definition of specific therapeutic targets. Experimental allergic encephalomyelitis (EAE) is a good...
| Summary: | Autoimmune diseases result from inappropriate self-reactivity by lymphocytes. The long-term goal is to generate specific therapies for autoimmune diseases of humans, the success of which hinges on the definition of specific therapeutic targets. Experimental allergic encephalomyelitis (EAE) is a good animal model for the human demyelinating autoimmune disease, multiple sclerosis (MS). Risk for these diseases stratifies by major
histocompatibility complex (MHC) allele, as well as by T
cell receptor (TCR) locus RFLP, in the case of MS. These
data suggest that (TCR-self peptide-MHC) complexes are
associated, possibly causally, with pathogenesis. This work
focused on the self peptide and TCR components of this
complex. One specific aim was to document and characterize
the T cell epitopes of the autoantigen, myelin basic protein
(MBP), in the EAE-susceptible mouse strain, B10.PL. Inbred
B10.PL mice which were immunized with self MBP in complete
Freund's adjuvant activated lymphocytes specific for
epitopes estimated by peptides MBP(NAc1-20), MBP(31-50), and
MBP(121-140). These mice generated the bulk of their immune
response to the MBP(NAc1-20) epitope. The responses to self
MBP immunization of B10.PL wildtype and MBP null "shiverer"
mice were compared, and it was found that MBP(12I-140) is
tolerogenic in animals which express MBP. A similar result
was observed in BALB/c wildtype and shiverer mice. These
data demonstrate that MBP is not a sequestered antigen, that
multiple epitopes tolerize T cells independently, and that
incomplete, rather than absent, tolerance is present in mice
susceptible to EAE. A second specific aim was to document
the degree of variation in the primate TCR Vβ 8 subfamily,
three members of which are adjacent to a BamHI RFLP
restriction site linked to multiple sclerosis (MS) disease
risk. Vβ 8.1 and 8.2 were compared in a number of primates.
It was found that the overall coding sequences, but not the
CDR coding sequences, were conserved compared with adjacent
non-coding flanking sequences. CDR coding sequences were
not demonstrably positively selected compared with noncoding
flanking sequences or with synonymous coding sequences. A comparison of unrelated normal humans failed to demonstrate any non-synonymous Substitutions within Vβ 8.1 and 8.2, and demonstrated a single non-synonymous Substitution in Vβ 8.3. These data demonstrate that germline Vβ 8 gene segments are conserved and minimally polymorphic, implying that final TCR protein diversity derives from other mechanisms. Occasional allelism has been demonstrated in other Vβ subfamilies, and our data does not rule out that certain TCR Vβ alleles may ultimately be found to contribute to autoimmunity disease risk.
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