Inhibition of NK cell activation by LLT1-mediated triggering of CD161.

<p>PBMC were isolated and co-cultivated for three hours with 293-mock or 293-LLT1 transfectants. Activation of NK cells was assessed by monitoring CD107a expression on gated CD3^-CD56⁺ and CD3^-CD56⁺CD161⁺/CD161^- cells. (A) Abrogation of inhibition by antibody-mediated blocking of CD161/LLT1 interactions. Co-cultivation of PBMC with 293 transfectants was performed in the presence of the anti-CD161 mAb 191B8 or an isotype-matched control antibody. (B) Frequency of activated NK cells after cultivation with 293-mock or 293-LLT1 cells. PBMC from nine individuals with CD161 TT and four carriers of CC were studied. (C) Diminished capacity of CD161 from CC carriers to inhibit NK cell activation. % Inhibition was calculated as follows: 100 - [(%CD107a⁺ NK cells in 293-LLT1 co-cultures / %CD107a⁺ NK cells in 293-mock co-cultures) x 100];*p<0.05 (Mann-Whitney). (D) LLT1 induced CD161 down-regulation on IL-12 activated NK cells. PBMC were co-cultured for three hours with either mock transfected 293 cells or cells expressing LLT1. CD161 expression was monitored on gated CD3^-CD56⁺ NK cells. Depicted histograms show CD161 expression in untreated NK cells (open) and after treatment with 293-LLT1 transfectants (filled histograms). The broken vertical line indicates the peak of CD161 observed in LLT1-treated NK cells from a TT individual. The graph summarizes data obtained in experiments using cells from five TT and three CC individuals (mean ± SEM).