Molecular associations involving CD 16, CD45 and ζ, and γ chains on human natural killer cells

Abstract

ζ (CD3‐ζ) and γ (FcεRIγ) chains associate with CD 16. the low affinity receptor for IgG (FcλRIII) on human NK cells and are essential for the cell surface expression of CDI6 and for CD16‐mediated effector functions. This study has investigated whether, on NK cells, molecules other than CD16 associate with ζ, and γ chains, as a method of identifying other NK cell surface molecules important in NK cell function. Cell surface biotinylated NK cells were lysed in digitonin, and the lysates immunoprecipitated with mAb to CD 16, ζ, and γ and the immunoprecipitates analysed by SDS‐PAGE. CD 16 mAb co‐precipitated ζ and γ chains (16 and 12kD. respectively) and in addition molecules of 24. 32–35, 100, 150 and 180–200 kD. Also, C, mAb co‐precipitated ζ chain, and molecules of 24–26, 32–35. 48, 50–66, 100, 150 and 180–200 kD; and γ co‐precipitated ζ, chain, and molecules of 24–26, 29, 32–35, 37, 45, 49, 50–66 and 100 kD. While significant amounts of ζ, and γ were co‐precipitated with CD 16, 10 to 12‐fold more ζ and γ were immunoprecipitated with their respective mAb. Furthermore, depletion of CD 16 from the lysate resulted in only a partial (10–12%) depletion of ζ, and γ indicating that only a relatively small proportion (10–12%) of these molecules are associated with CD 16. Interestingly, substantial amounts of molecules with electrophoretic mobility similar to CD16 (50–66 kD) were co‐precipitated with ζ, and γ chain mAb from lysates depleted of CD16. In contrast to NK cells where I, associated with a number of different molecules, the majority of ζ, in T cells was found to be associated only with the TCR: CD3 complex. NK cells showed a strong association between CD45, CD 16 and a 33 kD molecule and often a strong association of ζ, with CD l6, CD45 and an unidentified molecule of −150 kD. Our results show first, that CD16, ζ and γ each can be efficiently labelled by cell surface biotinylation, and second, that CD 16, C, and γ each can form a complex with each other, and with a number of additional molecules including a 33 kD molecule and CD45 potentially important in NK cell function.