Immunoglobulin .mu.- and .gamma.-ribonucleic acid sequences in thymocytes and splenocytes from normal and hyperimmune mice

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Abstract
The Ig H-chain RNA repertoire of mouse thymocytes was examined. Ig .alpha.-chain RNA sequences were previously reported in mouse thymocytes. These studies were extended to encompass .mu., .gamma.2b and .gamma.1 H-chain RNA sequences. .mu.-, .gamma.2b- and .gamma.1-m[messenger]RNA were purified from myelomas to 45, 22, and 54% purity, respectively. Each of these mRNA faithfully translated into the appropriate immunoprecipitable protein in a reticulocyte lysate translation system. The .gamma.1-mRNA translated into 2 major immunoprecipitable prodicts of about 52,500 and 51,000 daltons while .mu.- and .gamma.2b-mRNA yielded only a single major protein. Complementary[c]DNA prepared from the mRNA were used as hybridization probes and revealed the presence of about 70 .mu.-RNA sequences per average thymocyte as determined by hybridization kinetics, while .gamma.1 and .gamma.2b sequences were at the limits of detection. The .mu.-RNA sequences are present in the cytoplasm and are > 50% polyadenylated. Upon hyperimmunization of mice with sheep red blood cells, .gamma.1-RNA in splenocytes increased by about 100-fold while only slightly increasing in thymocytes. .mu. and .gamma.2b increased 2- to 3-fold in splenocytes and only slightly in thymocytes. The results argue against RNA sequences appearing in thymocytes due to contamination with peripheral plasma cells. The results involving .mu.- and .gamma.2b-RNA were confirmed with cloned cDNA probes. Thymocyte NA analyzed by Northern blots displayed bands of the same size as those in splenocyte RNA or in purified mRNA when hybridized to .mu., .gamma.2b and .alpha. cloned probes. Also, .kappa. L-chain RNA of the same size were found in spleen and thymus by using a cloned .kappa.-DNA probe. The results are consistent with the thymus containing .mu.-, .alpha.- and .kappa.- and small amounts of .gamma.1- or .gamma.2b-RNA coding for H and L-chain-like proteins which may play a role in T-cell function.