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P0, a major structural protein of peripheral myelin, is a homophilic adhesion molecule and maps to chromosome 1q22-q23, in the region of the locus for Charcot-Marie-Tooth neuropathy type 1B (CMT1B). We have investigated P0 as a candidate gene in two pedigrees with CMT1B and found point mutations which are completely linked with the disease (Z = 5.5, theta = 0). The mutations, glutamate substitution for lysine 96 or aspartate 90, are located in the extracellular domain, which plays a significant role in myelin membrane adhesion. Individuals with CMT1B are heterozygous for the normal allele and the mutant allele. Our results indicate that P0 is a gene responsible for CMT1B.

T lymphocyte lines specific for the peripheral nerve myelin protein P2 were selected from the lymph nodes of Brown Norway (BN) rats immunized with bovine P2 protein in complete Freund's adjuvant. These T cells expressed the W3/25+, OX8-phenotype and responded specifically to bovine P2 protein, but not to PPD or bovine basic protein, in T cell proliferation assays. When injected i.v. into syngeneic recipients, BN P2-specific T cell lines induced both clinical and histologic signs of experimental allergic neuritis (EAN), overcoming the resistance of this rat strain to actively induced EAN. Although the histopathology of the disease was indistinguishable from that seen in T cell-mediated EAN in the Lewis rat, disease onset was considerably later, 7 to 8 days after cell transfer, as opposed to 4 days in Lewis. This lag phase between inoculation and disease onset could not be further reduced even by raising the cell dose to 50 X 10(6) cells/host. The fine specificity of the T cell response to P2 differs between Lewis- and BN-derived T cell lines. At least one neuritogenic epitope for each strain was present in the cyanogen bromide-derived peptide CB2 (residues 21-113), as shown by the ability of CB2-specific T cell lines derived from each strain to transfer EAN to the appropriate host strain. However, neuritogenic BN T lines fail to mount a response to the sequence 53-78 (SP4), which encompasses an epitope that is neuritogenic for Lewis rats. These results demonstrate that the resistance of BN rats to actively induced EAN is not due to the lack of appropriate P2-specific autoreactive T cell clones in the normal T repertoire. Furthermore, the results suggest that two distinct epitopes of P2 are responsible for EAN in Lewis and BN rats.

— The S-100 protein fraction of pig and sheep brain was purified in 40 per cent yield by a modification of the procedure of Moore (1965), which avoided selective loss of S-100 components. The S-100 fraction of both pig and sheep is a mixture of proteins as indicated by acrylamide gel electrophoresis and N-terminal amino acid analysis. Differences in amino acid composition, electrophoretic heterogenity and N-terminal analysis were found. One fraction (fraction A) was isolated by DEAE-Sephadex chromatography from pig brain S-100 protein fraction. It was considered to be a single protein since it migrated as a single band on acrylamide gel electrophoresis and showed a single symmetrical peak during ultracentrifugal analysis. Only one N-terminal amino acid was detected in fraction A. The amino acid composition of this fraction showed minor but significant differences from that of the complete S-100 protein fraction from pig brain. The S-100 protein fraction of both species, as well as fraction A, had similar s20, w values and similar molecular weights (about 20,000) as indicated by gel filtration. These results, together with the immunological data obtained by other authors, suggest that the proteins of the S-100 fraction are closely related; the heterogeneity of the S-100 protein fraction may be of the same type as the lactate dehydrogenase isoenzymes.

A rat T cell line of the "helper" phenotype (W3/25-positive, OX 8-negative) has been derived from Lewis rats inoculated with P2 protein isolated from bovine PNS myelin. The line LiP2/A is exquisitely specific for P2 protein, exhibiting no reactivity to bovine basic protein or to PPD. In addition to responding strongly to the intact P2 protein, the line cells show some response to a synthetic peptide containing the neuritogenic amino acid sequence of P2 protein (SP-B, residues 66-78). Intravenous inoculation of naive rats with as few as 10(4) activated LiP2/A cells leads to the onset of mild clinical signs of experimental allergic neuritis. Higher doses of cells lead to more severe clinical disease. Histologic examination of clinically ill animals confirmed the disease as EAN. The pathologic lesions were confined to the PNS and spared the central nervous system. The lesions consisted of marked perivascular cuffs and infiltrates of inflammatory cells associated with marked degenerative changes--demyelination and some axonal degeneration.