On the role of CD3 delta chains in TCR gamma delta/CD3 complexes during assembly and membrane expression

The present study was performed in order to analyze whether T-cell receptor (TCR)/CD3 assembly, intracellular transport and surface expression are car ried in a similar way in o alpha beta -and gamma delta -T cells. By means o f optimal immunoprecipitation conditions with S-35-methionine/cysteine- or biotin-labelled TCR/CD3 proteins from alpha beta- or gamma delta -T-lymphom a-cell lines, as well as TCR gamma delta cDNA transfectants, it was found t hat CD3 delta chains associate less strongly with TCR gamma delta heterodim ers compared to TCR alpha beta heterodimers. This preferential reactivity o f CD3 delta chains appears to be structural and not owing to differences in gamma delta- versus alpha beta -T-cell intracellular environments. Our res ults are in accordance firstly, with data from CD3 delta -deficient mice, w hich have gamma delta -T cells but no alpha beta -T cells, secondly with th e suggested role of CD3 delta chains in the positive selection of alpha bet a -T cells, a process apparently not followed by gamma delta -T cells, and lastly with the differential roles of CD3 delta chains versus CD3 gamma cha ins, explaining the maintenance of two CD3 delta and CD3 gamma genes after the duplication from a CD3 delta/gamma gene present in avians. The impaired reactivity of CD3 delta chains with TCR gamma delta heterodimers seems to be owing to a less efficient association with TCR gamma chains. In contrast , CD3 delta chains interact as strongly with TCR delta chains as do CD3 gam ma chains with both TCR gamma and TCR delta chains. These data may explain, at the molecular levels, why surface TCR/CD3 expression levels are impaire d in gamma delta -T cells from CD3 gamma -deficient mice but not from CD3 d elta -deficient mice.