Changes In Leukocyte Distribution And T-cell Reactivity During Initial Military Training

Abstract

PURPOSE: Physiological stressors present during initial military training (IMT) may increase risk of illness and infection by suppressing immune function. This study aimed to improve insight into those relationships by characterizing changes in markers of innate and adaptive immune function during IMT. METHODS: Sixty U.S. Army infantry recruits (97% male) provided fasted blood and saliva samples at the beginning (PRE; week 0) and end (POST; week 22) of IMT. Peripheral leukocyte distribution was measured by flow cytometry, and T-cell and innate cell reactivity were measured by mitogen (anti-CD3/CD28 or lipopolysaccharide (LPS))-stimulated cytokine profiles in 48-hr whole blood culture. Latent reactivation of Epstein-Barr virus (EBV), varicella-zoster virus (VZV), and herpes simplex virus 1 (HSV1) was measured in saliva by qPCR. RESULTS: Lymphocyte percentage increased (+28%) while granulocytes (-15%) and monocytes (-13%) decreased PRE to POST (all P < 0.01). This lymphocytosis was driven by an increase in natural killer cells (+19%), and accompanied by decreases in B-cells (-9%) and T-cells (-5%; all P < 0.01). Within T-cell subsets, terminally differentiated CD4+ (+22%) and CD8+ (+30%) cells increased while those of effector memory CD4+ cells (-11%), effector memory CD8+ cells (-54%) and central memory CD8+ cells (-15%) decreased (all P ≤ 0.02). T-cell production of most measured cytokines following anti-CD3/CD28 stimulation increased from PRE to POST (P < 0.05). Conversely, stimulation with LPS resulted in reduced production of most measured cytokines (P < 0.05). Prevalence of EBV reactivation was higher POST (n=30) relative to PRE (n=19; P = 0.01), but neither VZV nor HSV1 reactivation was observed at either time point. CONCLUSION: Lymphocytosis, maturation of CD4+/CD8+ T-cell subsets, and heightened T-cell reactivity at POST collectively suggests an appropriate immune response to pathogen challenges during IMT. Though EBV reactivation was increased at POST, no evidence of VZV or HSV1 reactivation, which are more common during severe stress, was observed. Findings suggest that EBV reactivation during IMT was likely appropriately controlled in recruits and that immune-competence was relatively uncompromised at the end of IMT. Supported by USAMRDC. Authors’ views not official DoD or Army policy