Ia alloantigen(s) detected on thymocytes by use of a fluorescence-activated cell sorter.

With the increased sensitivity of detection of fluorescence made possible by a fluorescence-activated cell sorter (FACS), Ia antigen(s) have been demonstrated, although very small amounts, on murine thymocytes by using an indirect immunofluorescent technique. Absorption studies indicate that the Ia antigens detected on thymocytes are also present on spleen B cells, however, they do not rule out the possibility that certain Ia antigens may exist only on B cells. These studies suggest that the surface distribution and/or the decreased density of Ia antigens on thymocytes relative to peripheral B cells may preclude their demonstration by more conventional assays. Although these studies demonstrate Ia antigens on less than 50% of thymocytes, the percentage may in fact be much higher since current methods do not allow an upper limit to be assigned.