In most scientific investigations, the study of mechanism follows the
study of function. For example, alpha beta T cells were shown to be im
portant mediators of immunity before the interaction between the T cel
l receptor (TCR) and peptide-MHC complexes was understood. However, so
metimes the study of function follows from the study of mechanism. Res
earch of gamma delta T cell receptors falls into this category. The ga
mma chain of the TCR was first cloned in 1984, which then led to the d
iscovery of gamma delta T cells in 1985. Since then, research has focu
sed on understanding ligands of the gamma delta TCR with the hope of b
etter understanding the function of gamma delta T cells. An initial as
sumption was that gamma delta T cells, like alpha beta T cells, recogn
ize peptides bound to MHC molecules; however, recent data indicate tha
t gamma delta T cells are not biased towards MHC recognition in the sa
me way as alpha beta T cells. Although there are intriguing new insigh
ts, the specificity and function of gamma delta T cells remains a myst
ery.