STRUCTURAL-ANALYSIS OF LOW TCR-CD3 COMPLEX EXPRESSION IN T-CELLS OF AN IMMUNODEFICIENT PATIENT

Normal membrane expression of the T cell receptor (TCR) depends on the coordinated synthesis and assembly of all seven proteins composing the complex, i.e. the TCR-alpha and beta-chains, the CD3-gamma, delta, and epsilon-chains, and the zeta-zeta or zeta-eta-dimer. In an experimental TCR membrane-defective T cell variant (Sussman, J. L., Bonifacino, J. S., Lippincott-Schwartz, J., Weissman, A. M., Saito, T., Klausner, R. D., and Ashwell, J. D. (1988) Cell 52, 85-95) and in two siblings whose lymphocytes express only a low level of the TCR/CD3 complex (Alarcon, B., Berkhout, B., Breitmeyer, J., and Terhorst, C. (1988) N. Engl. J. Med. 319, 1203-1208), a defect in zeta-chain synthesis and/or assembly was thought to account for the defective membrane synthesis of the whole complex. We report on another immunodeficient patient whose T lymphocytes express the T cell receptor at one-tenth of normal fluorescence intensity and are not triggered to proliferate in vitro by anti-CD3 or anti-CD2 antibodies. Biochemical analysis of the patient's surface-iodinated peripheral blood lymphocytes failed to detect TCR-alpha and beta, or CD3-gamma, delta, and epsilon-proteins but revealed the presence of the zeta-homodimer (probably as a result of the high proportion of natural killer cells). In the cytoplasm, TCR-alpha and beta-proteins and the zeta-chain were detected, but, using monoclonal anti-CD3 antibodies, the CD3-gamma, delta, and epsilon-chains were not. In addition, the CD3-epsilon-chain was not detected with polyclonal antiserum in a verv sensitive Western blotting detection system. The zeta-chain was shown to be synthesized by the patient's T and natural killer cells. Northern blot analysis revealed normal levels of normal-size TCR-beta and CD3-gamma, delta-gene-specific mRNAs and decreased levels of TCR-alpha mARN; CD3-epsilon-gene transcripts were of abnormal size and present in lower than normal amounts. These findings suggest that this defect in T cell receptor-CD3 expression involves a mutation in the CD3-epsilon-gene leading to the synthesis of an abnormal and unstable CD3-epsilon-subunit.