Spontaneous cytotoxicity against virus-infected cells: relationship to NK against uninfected cell lines and to ADCC.

Cellular immunoadsorption and cold cell competition assays were used to examine the specificity of NK. Lymphocytes nonadherent to monolayers of cells persistently infected with Sendai virus (SV-HEp2) were almost totally depleted of NK against the uninfected tumor cell lines K562, MOLT-4, and HSB, as well as against SV-HEp2, when assayed immediately after separation. Lymphocytes adherent to SV-HEp2 monolayers were also partially depleted of NK against these targets. After overnight incubation, the nonadherent cells remained relatively depleted of NK against all targets, compared to controls. The adherent cells displayed a variable amount of activity, depending on the donor; in all cases, however, substantial NK activity was observed in this fraction against all targets, infected and uninfected. Exogenous interferon failed to augment the activity of the nonadherent lymphocyte fraction. Cellular immunoadsorption on monolayers of K562 or HSB was similarly found to partially deplete NK against SV-HEp2, as well as against the homologous cells. Cold cell inhibition studies showed that SV-HEp2 and, to a lesser extent, HEp2, could inhibit the lysis of K562; similarly, K562 could partially inhibit the lysis of SV-HEp2. We concluded that infected and uninfected target cells are lysed by overlapping populations of NK effector cells. In addition, the ADCC activity of SV-HEp2-adherent and nonadherent lymphocyte fractions was examined immediately after separation. Whereas the nonadherent lymphocytes were depleted of both ADCC and NK, the adherent lymphocytes were partially depleted of NK yet contained high levels of ADCC activity.