These studies were initiated to investigate monocyte regulation of polyclonal antibody responses of human peripheral blood lymphocytes stimulated by sonicates of periodontally associated bacteria. With pokeweed mitogen (PWM) as a positive reference, the role of monocytes in the peripheral blood lymphocyte response to Streptococcus sanguis and Wolinella HVS was examined by manipulating the number of monocytes and lymphocytes in culture. In comparison to PWM, optimal responses to the bacterial sonicates required very few monocytes (0.3% of the total cultured cells). Restoration of monocytes to physiological levels resulted in suppression of the response. PWM-stimulated responses were optimal at 5 to 15% monocyte content and were abolished after monocyte depletion. Individuals who were low responders or nonresponders to bacterial sonicates responded at normal levels after manipulation of monocyte concentration. Nonresponders produced normal levels of antibody when the monocyte concentration was reduced to 0.3% but were inhibited after monocyte reconstitution. The effects of monocyte concentration were tested over a wide dose range of bacterial sonicate and found to conform to the observed pattern throughout the dose range tested (10 to 1,000 micrograms/ml). The contrasting monocyte requirement of peripheral blood lymphocytes stimulated with PWM versus bacterial sonicates may reflect a quantitative difference in optimal macrophage concentration or may be due to a qualitative difference in lymphocyte-monocyte interactions in response to these activators
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