The immunoglobulin μ constant region gene is expressed in mouse thymocytes

Abstract

It has been a matter of controversy whether the functional capacity of T cells to discriminate between antigens is mediated via immunoglobulin, an immunoglobulin-like molecule, or by the product(s) of unrelated genes. The progenitors of immuno-globulin-secreting cells, B cells, express membrane-bound immunoglobulin as the antigen-specific receptor on their surface¹. For T cells, although products of immunoglobulin heavy chain variable region genes are implicated as receptor components^2–4, there has been no compelling immunochemical evidence for participation of either immunoglobulin light chains or heavy chain constant regions (see refs ^2–6 for the disparate views). Recently, using cloned immunoglobulin DNA sequences as hybridization probes, we have demonstrated that the immunoglobulin C_μ gene, but not the C_κ gene, is expressed as polyadenylated RNA in some B cell tumour (T lymphoma) cell lines⁷. Individual T lymphoma lines yielded up to three discrete μ RNA species of different sizes (1.9, 2.2 and 3.0 kilobases), each species being different in size from the major μ RNA species present in B lymphoma cells (2.4 and 2.7 kilo-bases)^7,8. We show here that cells from the normal mouse thymus contain μ RNA species, indistinguishable in size from those in T lymphoma cells, but contain little if any κ RNA.