Acute stress transiently activates macrophages and chemokines in cervical lymph nodes

Lymph nodes are vital for optimizing immune responses. Stress can induce several cellular and humoral immune responses. Acute restraint stress (RS) is a routinely used experimental procedure for studying psychological and/or physiological stress effects. Here, we determined the impact of RS on cervical lymph nodes in rats at the molecular and cellular levels. Stress was induced in male Sprague-Dawley rats by immobilization for 30, 60, and 120 min (RS30, RS60, and RS120, respectively) relative to a no-stress control (C) group. Expression of genes encoding chemokines CXCL1/CXCL2 (Cxcl1 and Cxcl2) and their receptor CXCR2 (Cxcr2) was analyzed at the mRNA level by reverse transcription-quantitative PCR (RT-qPCR) and microarray analyses. Immunohistochemistry and in situ hybridization were performed to determine the expression of these moieties along with the macrophage biomarker, CD68. Microarray analysis revealed that expression of 514 and 496 genes was upregulated and downregulated, respectively, in RS30. Cxcl1 and Cxcl2 expression showed a 23- and 13-fold increase, respectively, in RS30 relative to the C group. Expression of Cxcr2 was upregulated by approximately 1.6-fold in RS30 relative to the C group. Gene ontology analysis of three upregulated genes induced by RS30 suggested that they may be responsible for the cytokine network, inflammation, as well as leukocyte chemotaxis and migration. RT-qPCR analysis indicated that the mRNA levels of Cxcl1 and Cxcl2 significantly increased in RS30 but reverted to normal levels in RS60 and RS120. Cxcr2 mRNA level also increased significantly in RS30 and RS120 relative to the C group. RS-induced CXCL1-immunopositive cells corresponded to B/plasma cells, while CXCL2-immunopositive cells corresponded to endothelial cells of the high endothelial venules. Stress-induced CXCR2-immunopositive cells corresponded to macrophages. Psychological and/or physiological stress induces acute stress response and immunoreactive microenvironment in cervical lymph nodes, and the CXCL1/CXCL2-CXCR2 axis is pivotal in acute stress response. In this study, we aimed to elucidate the effects of acute stress using our experimental model, on the cervical lymph nodes, as a representative secondary lymphatic organ, with respect to changes in expression levels and immunochemical characteristics of macrophages, erythrocytes, CXCL1, CXCL2, and CXCR2 in rats.