Computer analysis of defined populations of lymphocytes irradiated in vitro. II. Analysis of thymus-dependent versus bone marrow-dependent cells.

Three uniform populations of T and B cells exposed to varying amounts of x-irradiation are examined utilizing computer-assisted morphometric analysis. These populations are: thoracic duct lymphocytes (TDL) from congenitally athymic (nude) mice (B cells); TDL from CBA mice treated with anti-Ig plus complement (T cells); and computer-selected untreated T cells from CBA TDL. Irradiated B cells show a more even dispersion of the nuclear chromatin and a dose-dependent increase in relative nuclear area beginning with the lowest dose evaluated (50 rads); no significan change in total optical density (OD) is demonstrable over the dose range evaluated (0 to 2000 rads). Anti-Ig-treated irradiated T cells demonstrate an initial shift toward lower OD values as a function of dose followed by a marked rise of OD values at 2000 rads, where numerous densely staining Feulgen-positive aggregates are identified. The relative nuclear area of this cell population also shows a biphasic response to radiation injury with an initial increase at the lower dose levels followed by a progressive decline to approximate control levels at 2000 rads. This effect is mirrored by the alteration in total OD which, after a decrease at low dose levels, approximates control values at 2000 rads. The computer-selected T cells show little change in OD values at the low-dose levels but show a marked increase in the more densely staining Feulgen-positive material following 2000 rads. This population reveals no apparent change in either relative nuclear area or total OD as a function of dose. Thus, untreated computer-selected T cells exhibit remarkably little evidence, morphologically, of radiation injury of doses associated with pronounced alterations on the part of B cells. In addition, treatment of a mixed cell population (CBA TDL) with anti-Ig plus complement to remove the B cells appears to alter the response of the residual T cells to radiation injury. These results, in conjunction with recent evidence to support the concept that T cells possess surface Ig, suggest that an Ig-anti-Ig interaction may alter the radiosensitivity of T cells.