Immunoglobulin messenger RNAs of T lymphocytes

The potential of T cells to synthesize immunoglobulins was investigated in thymus cells obtained from young mice. Such thymocytes contained very low levels of B cell contamination. It was found by hybridization of thymus RNA with complementary DNAs (cDNAs) synthesized from myeloma κ and H chain mRNAs that these T cells contain relatively large amounts of κ, μ, and at RNAs. RNAs for γ1 and γ2b seem to be absent. The Ig RNAs of thymus form stable hybrids with B cell derived cDNAs and are present at levels comparable (50%) to those found for the same RNAs in spleen. The thymic κ RNA is of the same size as B cell κ RNA. It is present in 99% of thymus cells as shown by in situ hybridization. The T cell κ RNA is a true messenger RNA, since (1) it is translatable into κ chains in a cell free system and (2) it is found to be enriched in the protein synthetic apparatus of membrane bound and free polyribosomes within T cells. Kappa and H chain mRNAs were also found to be translated by live T cells in short term culture. After activation by concanavalin A, thymus cells doubled the synthesis of immunoglobulins, while the initially very low numbers of contaminating B lymphocytes and plasma cells were further reduced 10- to 30-fold. The combined experimental evidence strongly indicates that T cells have the potential for the synthesis of immunoglobulins which may have receptor and effector functions. The question of whether T cell Igs are truly identical to B cell Igs is discussed in light of findings of our and other laboratories.