932 MODULATION BY T CELL SUBSETS OF MYELOID STEM CELLS

Abstract

It has been shown that T lymphocytes modulate in vitro myeloid colony formation (CFU-C). The current studies were aimed at determining whether human T cell subsets separated on the basis of presence or absence of Fc receptors for IgG have differential effects on CFU-C. T cells prepared by nylon wool filtration of Ficoll-Hypaque separated peripheral blood leukocytes (PBL) were incubated with IgG coated ox erythrocytes (EA_G). Cells rosetting with EA_G (T_G +) were separated from non-rosetting cells (T_G−) by gradient separation. T_G− cells were further separated by sheep erythrocytes (E)- rosette sedimentation into E-RFC+ and E-RFC-cells. The latter, enriched in CFU-C, were pre-incubated alone (control), or in the presence of T_G + or T_G− cell fraction for 18 hours, and then plated in methylcellulose in the presence of fibroblast conditioned medium as a source of colony stimulating factors. In four experiments, those pre-incubated with T_G− cells showed a 388%, 246%, 149%, and 262% increase over the controls in the number of myeloid colonies formed (p<0.001). By contrast, those pre-incubated with T_G+ cells showed an 81%, 94%, 15%, and 91% reduction of the control colony number (p<0.01). These findings suggest that T cell subsets have opposing effects on myeloid colony forming cells. Those lacking Fc receptors for IgG stimulate CFU-C, whereas those expressing Fc receptors for IgG inhibit CFU-C.

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