Changes in the cellular component of the human innate immunity system in short-term isolation

Abstract

A systemic approach in the evaluation of the various components of the immune system gave an opportunity to identify a number of characteristics of adaptive changes, including the quantitative and functional changes in both innate and adaptive immunity in response to space flight. Among them the most important are the changes in the system of Toll like receptors (TLRs), namely, the decrease in the content of circulating monocytes and granulocytes expressing TLR2, TLR4, TLR6, and inhibition of T-cells functional potential. However, a fundamentally important problem of revealing the complex of intermolecular and intercellular interactions during the immune response development under space fight conditions in an organism as a whole still remains unsolved. By now there exists quite strong evidence that dendritic cells (DCs) play the important role in linking the innate and adaptive immunity through their characteristic expression patterns of TLRs and cytokine production. In this study we examined the number of circulating plasmacytoid DCs (pDCs) and monocytes expressing signaling PRRs in 6 healthy participants of the “SIRIUS-17″ project. Whole blood was collected at prior, during and post isolation periods from three male and three female volunteers aged 27 to 43 who spent 17 days in permanent isolation in an enclosed habitat consisting of hermetically sealed interconnecting modules at the Institute for Biomedical Problems (IBMP) in Moscow. Results of the investigation showed a distinct effect of short-term isolation on the immune system ability to mobilize. Although no significant changes in the percentages of cells which expressed surface TLRs (TLR1, TLR2, TLR4, TLR5 and TLR6) and endosomal TLRs (TLR3, TLR8 and TLR9) were noted, the percentage of pDCs (CD14-/CD16-CD123 + CD85k+) significantly increased on day 7 of the experiment compared with the baseline. These changes were independent of gender of volunteers. On the first day of recovery period the levels of TLRs and pDCs were lower than before the isolation almost in all volunteers, however observed changes in pDCs were not statistically significant. These data suggest that, unfavorable factors of a space flight make immune system function differently compared to the normal conditions. This mobility of the immune system allows adaptation to the constantly fluctuating environment. However, the adaptive restructuring requires mobilization of functional resources at an early stage of adaptation, which can lead to depletion of reserve capabilities of the immune system.