We explored mechanisms involved in B cell self-tolerance against brain autoantigens in a double-transgenic mouse model carrying the Ig H-chain (introduced by gene replacement) and/or the L-chain kappa (conventional transgenic) of the mAb 8.18C5, specific for the myelin oligodendrocyte glycoprotein (MOG). Previously, we demonstrated that B cells expressing solely the MOG-specific Ig H-chain differentiate without tolerogenic censure. We show now that double-transgenic (THkappa(mog)) B cells expressing transgenic Ig H- and L-chains are subjected to receptor editing. We show that in adult mice carrying both MOG-specific Ig H- and L-chains, the frequency of MOG-binding B cells is not higher than in mice expressing solely the transgenic Ig H-chain. In fact, in THkappa(mog) double-transgenic mice, the transgenic kappa(mog) L-chain was commonly replaced by endogenous L-chains, i.e., by receptor editing. In rearrangement-deficient RAG-2(-) mice, differentiation of THkappa(mog) B cells is blocked at an immature stage (defined by the B220(low)IgM(low)IgD(-) phenotype), reflecting interaction of the autoreactive B cells with a local self-determinant. The tolerogenic structure in the bone marrow is not classical MOG, because back-crossing THkappa(mog) mice into a MOG-deficient genetic background does not lead to an increase in the proportion of MOG-binding B cells. We propose that an as yet undefined self-Ag distinct from MOG cross-reacts with the THkappa(mog) B cell receptor and induces editing of the transgenic kappa(mog) L-chain in early immature B cells without affecting the pathogenic potential of the remaining MOG-specific B cells. This phenomenon represents a particular form of chain-specific split tolerance.

Using homologous recombination in embryonic stem cells, we have generated mice with a null mutation in the gene encoding the myelin-associated glycoprotein (MAG), a recognition molecule implicated in myelin formation. MAG-deficient mice appeared normal in motor coordination and spatial learning tasks. Normal myelin structure and nerve conduction in the PNS, with N-CAM overexpression at sites normally expressing MAG, suggested compensatory mechanisms. In the CNS, the onset of myelination was delayed, and subtle morphological abnormalities were detected in that the content of oligodendrocyte cytoplasm at the inner aspect of most myelin sheaths was reduced and that some axons were surrounded by two or more myelin sheaths. These observations suggest that MAG participates in the formation of the periaxonal cytoplasmic collar of oligodendrocytes and in the recognition between oligodendrocyte processes and axons.

T-cell receptors and T-cell subsets were analysed in T-cell receptor transgenic mice expressing alpha and beta T-cell receptor genes isolated from a male-specific, H-2Db-restricted CD4-8+ T-cell clone. The results indicate that the specific interaction of the T-cell receptor on immature thymocytes with thymic major histocompatibility complex antigens determines the differentiation of CD4+8+ thymocytes into either CD4+8- or CD4-8+ mature T cells.

A specific polyclonal antibody has been raised against a basic cytoplasmic protein (p27) which is induced by serum in growth-arrested NIH 3T3 cells but is constitutively expressed in nonestablished fibroblasts. Immunoblotting analysis and [35S]methionine labeling show that p27 is absent in tissues and established cell lines of different types. However, it is present in fibroblasts from human, rat, mouse, and chicken origin and is highly conserved as determined by two-dimensional gel electrophoresis. Double immunofluorescence shows that p27 colocalizes with actin filaments. These observations would suggest that p27 is an actin-associated protein expressed in nonestablished fibroblasts.

The nonhistone protein pattern of four murine teratocarcinomas with different capacities for differentiation were compared: a multidifferentiated teratocarcinoma OTT2289, a nondifferentiated teratocarcinoma OTT2158, a teratocarcinoma-derived rhabdomyosarcoma TDR114, and a teratocarcinoma-derived neuroblastoma TDN2151. Their nonhistone proteins (NHP) were separated by differential salt extraction and hydroxyapatite chromatography into three fractions, NHP-I, NHP-II and NHP-III. Comparison of the NHP fractions by twodimensional gel electrophoresis in combination with a sensitive silver staining method reveals that there are several tumour line specific proteins in each NHP fraction. We suggest that specific NHP, which can be used as biochemical markers for each of the four investigated tumour lines, may be involved in cell lineage specific control of gene expression.