Human blood leukocytes from three subjects who had been contact sensitized to dinitrochlorobenzene were used in direct and indirect leukocyte-adherence-inhibition (LAI) reactions in an attempt to elucidate the cellular mechanism of reactivity. The leukocytes were separated and purified by standard procedures. In direct LAI, only T cells or populations containing T cells gave positive reactions (significantly reduced adherence) with the antigen. Supernatants from suitable leukocyte-antigen mixtures contained a soluble leukocyte-adherence-inhibition-factor (LAIF) that reduced the adherence of normal leukocytes. Only T cells or populations containing T cells were active in LAIF production; B cells, granulocytes, and monocytes were inactive. The cellular requirement for the action of preformed LAIF was not restricted: all major types of blood leukocytes were susceptible to its effect.

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This work was supported by the Queensland Cancer Fund and the National Health and Medical Research Council.

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