LYMPHOCYTE-DERIVED CYTOKINES AUGMENT MACROPHAGE TUMOR-NECROSIS-FACTOR-ALPHA AND INTERLEUKIN-6 SECRETION DURING EXPERIMENTAL GRAM-NEGATIVE BACTERIAL SEPSIS

Although lymphocyte-derived cytokines are known to augment macrophage cytokine production in vitro, their effect on macrophage tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) secretion during gram-negative bacterial sepsis has not been characterized. The purpose of this study was to examine the effect of lymphocyte-derived cytokines on macrophage TNF-alpha and IL-6 secretion during gram-negative bacterial peritonitis. To examine this problem, uninfected and infected mice were studied. Mice were infected with Escherichia coli 0111:B4 and two subgroups were examined consisting of those pretreated iv 1 hr prior to bacterial challenge with either (1) saline or (2) anti-E. coli 0111:B4 LPS mAb 2A3, the latter administered to abrogate the effects of LPS in vivo. Thus, three groups of mice were studied in relation to pretreatment and infectious challenges: (1) saline/saline (control); (2) saline/E. coli (saline); and (3) mAb 2A3/E. coli (mAb 2A3). Nonadherent splenocytes (>95% lymphocytes by histologic staining criteria) harvested 16 hr later from mice in each group were incubated in culture ex vivo for 3 hr to obtain supernatants containing lymphocyte-derived cytokines. These supernatants containing lymphocyte-derived cytokines then were incubated in vitro with naive splenic macrophages with or without E. coli 0111:B4 LPS. Macrophage TNF-alpha and IL-6 levels were determined using L929 and B9 bioassays. Lymphocyte-derived cytokines obtained 16 hr after infection from mice pretreated with saline significantly stimulated TNF-alpha and IL-6 secretion compared to those obtained from uninfected mice (TNF-alpha, 525 +/- 67 pg/ml versus 16 +/- 03 pg/ml, P < 0.001; IL-6, 19.2 +/- 7.7 ng/ml versus 1.5 +/- 0.0 ng/ml, P < 0.05) and synergistically enhanced macrophage TNF-alpha secretion in combination with LPS compared to that in medium (1601 +/- 378 pg/ml versus 850 +/- 146 pg/ml, P < 0.05). Pretreatment of infected animals with anti-LPS mAb 2A3 blocked this effect (525 +/- 67 pg/ml versus 183 +/- 73 pg/ml, P < 0.01; 1601 +/- 378 pg/ml versus 791 +/- 46 pg/ml, P < 0.05). Interferon-gamma (IFN-gamma) concentrations in the lymphocyte-derived cytokines of all groups were <35 pg/ml. Thus, LPS released during infection induces lymphocytes to secrete cytokines other than IFN-gamma that may act to amplify the host cytokine response. Characterization of the cytokines responsible for this phenomenon may prove important in further delineating the pathophysiology of the host septic response. (C) 1995 Academic Press, Inc.