Mumps virus-induced enhancement of the in vitro cytotoxicity of cord blood lymphocytes.

Purified lymphocytes from the umbilical cord of healthy donors (CBL) displayed lower natural cytotoxicity (NK) and antibody-dependent cellular cytotoxicity (ADCC) than peripheral blood (PBL) from adult donors. In contrast, CBL treated with small amounts of UV-inactivated or live mumps virions expressed the same level of enhanced cytotoxicity (virus-dependent cytotoxicity (VDCC)) against non-infected target cells as PBL. For individual CBL donors there was no correlation between the level of NK and VDCC, indicating involvement of partly distinct effector cell populations. The heterogeneity of the effector cells active in VDCC was confirmed by cell fractionation experiments. The major CBL effector cells in NK and ADCC were found in 'non-T' lymphocyte fractions and/or in fractions containing cells with high-avidity receptors for IgG. In contrast, CBL fractions consisting of about 100% lymphocytes bearing T-cell markers and depleted of Fc gamma R+ cells were strongly cytotoxic in VDCC when T24 cells (human bladder carcinoma) were the targets. With two other target cell types of similar susceptibility to VDCC, the cytotoxic activity of T-cell-containing fractions was less pronounced, indicating that the target cells play an active role in effector cell selection. The surface marker profiles of the VDCC effector cells were the same for CBL and adult PBL. Incubation of CBL with UV-inactivated virions usually gave no significant stimulation of DNA synthesis above that seen in virus-free controls. Taken together, our results suggest that neither specific recognition of viral antigen by T cells nor mitogenic effects of viral material are involved in VDCC generation.