SUPPRESSION OF SKELETAL MUSCLE INTERLEUKIN-6 ALTERS CIRCULATORY CYTOKINE AND LEUKOCYTE TRAFFICKING IN SEPTIC MICE

Interleukin‐6 (IL‐6) is one of the major cytokines released by skeletal muscle in response to blood pathogens. Nevertheless, the contribution of IL‐6 secreted by skeletal muscle (skmIL‐6) to innate immunity is not well understood. We utilized a floxed IL‐6 knockout mouse crossed with a skeletal muscle inducible CRE mouse to evaluate the contribution of skeletal muscle IL‐6 secretion to the circulatory cytokine profile and leukocyte trafficking in septic mice. Sepsis was induced using intraperitoneal injection of a standardized dose of cecal slurry (CS) collected from donor mice. METHODS Twenty‐four animals were studied at 6 and 12 hours after CS injection and plasma cytokines were measured using multiplex array. Cell differential counts were performed on blood, peritoneal lavage (PL), spleen and bone marrow. Mice in which the recombination of CRE was induced with raloxifene (skmIL‐6 −/− ) were compared to sham strain‐match controls (skmIL‐6 +/+ ). RESULTS At the 6‐hour time‐point after CS injection, the skmIL‐6 −/− mice demonstrated significant reductions in INF‐d (skmIL‐6 +/+ = 21 ± 8 vs. skmIL‐6 −/− 7 ± 4, P < 0.01), IL‐5 (skmIL‐6 +/+ = 232 ± 43 vs. skmIL‐6 −/− 139 ± 52, P < 0.02), IL‐9 (skmIL‐6 +/+ = 128 ± 82 vs. skmIL‐6 −/− 22 ± 31, P < 0.02), IL‐10 (skmIL‐6 +/+ = 10846 ± 4080 vs. skmIL‐6 −/− 3350 ± 1456, P < 0.05), MIP‐1a (skmIL‐6 +/+ = 1054 ± 398 vs. skmIL‐6 −/− 477 ± 570, P < 0.05), MIP‐1b (skmIL‐6 +/+ = 2576 ± 613 vs. skmIL‐6 −/− 1432 ± 808, P < 0.05), and TNFa (skmIL‐6 +/+ = 77 ± 40 vs. skmIL‐6 −/− 29 ± 10, P < 0.01). At 12 hours, the only observed effect was a reduction in RANTES (skmIL‐6 +/+ = 61 ± 7 vs. skmIL‐6 −/− 37 ± 7, P < 0.05). In PL, 6 hours after cecal slurry injection, total leukocyte counts were unaffected. However, the %neutrophils was elevated from 21% in controls to 37% (P<0.0002) in skmIL‐6 −/− . Lymphocytes dropped from 15 to 5% (P<0.002) and basophils dropped from 3.8 to 2% (P<0.01). At 12 hrs post cecal slurry injection, total leukocytes remained unchanged between skmIL‐6 −/− and controls, but in PL neutrophils remained elevated (59% vs 45%, P=0.05), %lymphocytes were unchanged, but %monocytes increased from 9 to 13%, (P = 0.02); %eosinophils and %basophils were reduced (P < 0.03 and <0.02, respectively). There were no statistically significant differences between groups in the cell differential counts in blood, bone marrow or spleen. There were also no differences cell differentials in any tissue between raloxifene‐treated and untreated CRE mice. CONCLUSIONS Inhibition of IL‐6 production by skeletal muscles suppressed circulatory cytokines and chemokines required to provide immunity against polymicrobial sepsis. Importantly, regulation of inflammatory cells and the timing of their recruitment to the primary site of infection (i.e. the peritoneum in the cecal slurry model) was dependent on skeletal muscle IL‐6. Most of the observed changes occurred 6 hours after induction of polymicrobial sepsis which is consistent with skeletal muscle IL‐6 being required for the early innate immune response in this model. These effects appear to be independent of the influence of raloxifene, the estrogen receptor activator, or CRE. Support or Funding Information Supported by NIGMS1R01GM118895‐01 . This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .