Evidence that T colony formation is a property of T mu (helper) lymphocytes

The T-colony-forming capacity of different T lymphocyte subsets was studied in normal peripheral blood. Unfractionated lymphocytes (after 'Lymphoprep' separation) gave rise to a mean of 150 +/- 27 . 7 s.d. T colonies per 1 x 10(5) cells, while purified T lymphocytes by sheep RBC rosetting formed 110 +/- 32 . 2 colonies. Two subpopulations of T lymphocytes were further isolated according to the presence of Fc receptors for IgG (T gamma) or IgM (T mu) by ox RBC rosetting. T gamma cells were found to have a very low or absent T colony-forming capacity (23 +/- 26 . 2), while T mu cells produced normal colony numbers (106 +/- 28 . 4). Co-culture experiments showed that T gamma cells do not inhibit the T colony growth of normal T cells in our system. Our findings indicate that in human peripheral blood not all T lymphocytes are capable of forming T colonies and that this property is confined to the T mu (helper) lymphocyte subset.