No abstract

An essential property of the immune system is its ability to generate great diversity in antibody and T-cell immune responses. The genetic and molecular mechanisms responsible for the generation of antibody diversity have been investigated during the past several years. The gene for the variable (V) region, which determines antigen specificity, is assembled when one member of each of the dispersed clusters of V gene segments, diversity (D) elements (for heavy chains only) and joining (J) segments are fused by DNA rearrangement. The cloning of the beta-chain of the T-cell antigen receptor revealed that the organization of the beta-chain locus, which is similar to that of immunoglobulin genes, is also composed of noncontiguous segments of V, D, J and constant (C) region genes. The structure of the alpha-chain seems to consist of a V and a C domain connected by a J segment. We report here that the human T-cell receptor alpha-chain gene consists of a number of noncontiguous V and J gene segments and a C region gene. The V region gene segment is interrupted by a single intron, whereas the C region contains four exons. The J segments, situated 5' of the C region gene, are dispersed over a distance of at least 35 kilobases (kb). Signal sequences, which are presumably involved in DNA recombination, are found next to the V and J gene segments.

By using an indirect immunofluorescence technique, the presence of host cell derived H-2K, H-2D, and Ia alloantigens on donor cells recovered from recipient spleens after a graft-versus-host response (GVHR) was demonstrated. Mapping studies indicated that only host K, D, and I-A region gene products could be identified on the donor cells. Host I-E/C- and I-J-subregion products were not absorbed by donor cells. Treatment of activated donor cells with anti-Ly sera plus C' revealed that donor cells carrying host Ia antigens have a Ly-1+,2-,3- phenotype, whereas donor cells carrying H-2K and H-2D host antigens have a Ly-1-,2+,3+ phenotype. A GVHR that resulted from only an I-region incompatibility was suppressed by the injection of recipient mice with an anti-Ia antiserum directed against self Ia antigens. The degree of suppression was proportional to the amount of anti-Ia antiserum administered.

The phylogenetic relationships of six species of black flies were investigated using the hybridization of iodinated unique DNA sequences. The thermal stability of these labelled hybrids allowed the construction of a phylogenetic tree based on base mismatch between chains of the heterologous duplex.