Cell populations in leucocyte adherence inhibition: requirement for T lymphocytes with IgG Fc receptors

The subset identity of T lymphocytes participating in the leucocyte adherence inhibition (LAI) reaction was investigated. Humans were immunized with keyhole limpet haemocyanin (KLH) and their cellular immunity was tested by means of the haemocytometer variant of the LAI method. Their lymphocytes were fractionated by rosetting methods employing neuraminidase-treated sheep erythrocytes and IgG- or IgM-coated ox erythrocytes. The T lymphocytes rosetted by IgG-coated ox cells (T gamma) reacted with KLH to give specific LAI reactions. Non-T gamma cells failed to react. The T gamma cells released a lymphokine which caused an LAI reaction of T lymphocytes from non-immunized donors. Immune non-T gamma cells, when incubated with KLH yielded inactive supernates. The normal cells which gave positive LAI responses to the lymphokine also proved to belong exclusively to the T gamma subclass. Cells positively selected with IgM-coated ox cells (T micro) were inactive while the non-T micro lymphocytes behaved like the T gamma cells. It was shown that the activity was confined to the T gamma subset throughout the time course of a primary immune response. Thus, LAI reactivity appears to be a property of a very small subclass of lymphocytes which communicate with each other by means of a soluble factor.