Presentation of a soluble bacterial antigen and cell-surface alloantigens by large granular lymphocytes (LGL) in comparison with monocytes.

The ability of large granular lymphocytes (LGL) to function as antigen-presenting cells (APC) in the proliferative response to the soluble bacterial antigen streptolysin O (SLO) was investigated. Despite the fact that a subset of LGL isolated by sorting peripheral blood lymphocytes with the B73.1 monoclonal antibody on a fluorescence-activated cell sorter (FACS-IV) expressed MHC Class II molecules of the DP, DQ and DR subregion loci, presentation of SLO by LGL was not demonstrated. Thus, T-cell populations containing LGL but carefully depleted of monocytes, isolated either by sorting using the FACS-IV or by SRBC-rosetting, were unresponsive to antigenic stimulation with SLO. Application of exogenous interleukin-1 to FACS-IV-isolated LGL-containing T-cell populations did not elicit presentation of SLO by the LGL. In vitro activation with phytohaemagglutinin and interleukin-2, which induced Class II expression in T-cell populations, resulted in an increased expression of Class II molecules of the DP, DQ and DR specificities on LGL. Although such activated T-cell and LGL populations were incapable of presenting SLO to freshly isolated antigen-non-responsive T cells, both activated populations were able to act as stimulators in an allogeneic mixed lymphocyte reaction. The ability of highly Class II-positive activated LGL to present membrane-bound antigens suggests that their inability to present a soluble antigen may be related to the absence of effective antigen sequestration and/or processing mechanisms.