Effects of bacterial lipopolysaccharide on the induction and expression of cell-mediated immunity. II. Stimulation of the efferent arc.

The delayed-type hypersensitivity (DTH) produced by subcutaneous or intravenous immunization of mice with sheep red blood cells (SRBC) is mediated by T cells in cooperation with accessory cells (monocytes). Different effects of bacterial lipopolysaccharide (LPS) on this T cell activity were found at different stages of the immune response. a) T cell activity was enhanced by LPS given 1 to 3 days after sensitization. Enhancement, which was most marked when treatment was given on the 2nd day of the immune response, did not occur unless LPS was introduced into a site that drains to the responding lymph node. This stimulatory effect was dose dependent. b) A similar effect on the response to intravenous immunization caused DTH to appear transiently in mice given a T cell-blocking dose (10-9) of SRBC. c) DTH was suppressed by LPS given at the height of the T cell response (day 4). This effect, which was short lived and reversible, was due to the action of LPS on the accessor cells needed for the expression of DTH. Treatment of recipients with LPS completely blocked the adoptive transfer of DTH to both normal and spenectomized mice. The ability to react was regained slowly, but it returned promptly to splenectomized recipients. LPS has clearly more than one effect on the expression of cell-mediated immunity because it affects specific and non-specific mediator cells in different ways.