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 necrosi s factor-alpha (TNF-alpha) and interleukin-6 (IL-6) secretion during g ram-negative bacterial sepsis has not been characterized. The purpose of this study was to examine the effect of lymphocyte-derived cytokine s on macrophage TNF-alpha and IL-6 secretion during gram-negative bact erial peritonitis. To examine this problem, uninfected and infected mi ce were studied. Mice were infected with Escherichia coil 0111:B4 and two subgroups were examined consisting of those pretreated iv 1 hr pri or to bacterial challenge with either (1) saline or (2) anti-E. coil 0 111: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 p retreatment and infectious challenges: (1) saline/saline (control); (2 ) saline/E. coil (saline); and (3) mAb 2A3/E. coil (mAb 2A3). Nonadher ent splenocytes (>95% lymphocytes by histologic staining criteria) har vested 16 hr later from mice in each group were incubated in culture e x vivo for 3 hr to obtain supernatants containing lymphocyte-derived c ytokines. These supernatants containing lymphocyte-derived cytokines t hen were incubated in vitro with naive splenic macrophages with or wit hout E. coli 0111:B4 LPS. Macrophage TNF-alpha and IL-6 levels were de termined using L929 and B9 bioassays. Lymphocyte-derived cytokines obt ained 16 hr after infection from mice pretreated with saline significa ntly stimulated TNF-alpha and IL-6 secretion compared to those obtaine d from uninfected mice (TNF-alpha, 525 +/- 67 pg/ml versus 16 +/- 03 p g/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 v ersus 850 +/- 146 pg/ml, P < 0.05). Pretreatment of infected animals w ith 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 du ring infection induces lymphocytes to secrete cytokines other than IFN -gamma that may act to amplify the host cytokine response. Characteriz ation of the cytokines responsible for this phenomenon may prove impor tant in further delineating the pathophysiology of the host septic res ponse. (C) 1995 Academic Press, Inc.