Ly-18, a new alloantigen present on cytotoxic T cells and controlled by a gene(s) to the Igh-V locus.

Antiserum raised in allotype-congenic mice recognizes a T cell differentiation antigen designated Ly-18. This antiserum was raised by immunization of (CB.20 x CBA-Igh-1b)F1 mice with secondary BALB/c anti-CBA allospecific cytotoxic cells. This antigenic specificity is expressed on cytotoxic T cells but not on cells proliferating in an MLR, plaque-forming cells specific for SRBC, or resting lymphoid cells. The expression of Ly-18 is controlled by gene(s) linked to the VH gene complex of Igh-1 allotype strains. There is no evidence at present for MHC gene control. Unlike other putative antibodies against antigen receptors, anti-Ly 18 does not block cytotoxicity. In addition, Ly-18 expression is not altered by the antigenic specificity of the Igh-1 effector. We conclude Ly-18 is a differentiation antigen present on a subpopulation of activated T cells. The gene(s) that codes for expression of Ly-18 is linked to the expression of Igh-1 genes.