Leukocyte-adherence inhibition: a specific assay of cell-mediated immunity dependent on lymphokine-mediated collaboration between T lymphocytes.

The leukocyte-adherence inhibition (LAI) assay was studied to determine its immunologic relevance and identify the cell populations on which it depends. Two systems were employed: peripheral blood leukocytes from humans immunized with KLH, and lymph node cells from rats immunized with DNP-BCG. In both cases, LAI responses appeared about 3 to 4 days after immunization, reached a peak about 3 to 4 weeks later, and diminished thereafter. Reimmunization resulted in a booster-like response. LAI analysis in both systems showed dose-response dependency. Responses could be elicited only with the immunizing antigen. Virtual depletion of phagocytic cells had no effect on the response. E-rosette-forming cells gave an excellent response to KLH and also produced an active supernatant (lymphokine). Cells not forming spontaneous E-rosettes were inactive and could not produce active supernatants. Only those nonimmune cells that formed E-rosettes could respond to active supernatants. Thus, the LAI response is a specific indicator of cell-mediated immunity. T lymphocytes probably are required both at the antigen-reactive stage and at the stage of responding to the T cell-dependent lymphokine.