THE diverse functions of T lymphocytes in the defense of the host are mediated by multiple subpopulations that are often classified by the pattern in which they express surface structures. Most mature, post-thymic T cells bear the alpha/beta form of the T-cell receptor for antigen (TCR α/β). These cells also bear either CD4 or CD8 — glycoproteins characteristic of the helper-inducer and suppressor-cytotoxic subpopulations, respectively. A minor subpopulation of circulating T cells bears an alternative, gamma/delta form of the T-cell receptor for antigen (TCR γ/δ), but most of these cells express neither CD4 nor CD8.¹ Both TCR α/β and TCR . . .