Comparing antibody profiles to upper respiratory tract viruses in elite combat soldiers during training and their support staff

Introduction: During the first year of combat training, soldiers of elite units are under intense physical and mental stress. The antibody response to influenza vaccination or exposure has been reported to be enhanced in individuals that are seropositive for cytomegalovirus (CMV). To investigate the effect of stress and extensive physical training on the immune system, and the interplay between antibodies to different viruses, we longitudinally profiled changes in antibodies to upper respiratory tract viruses and cytokine profiles in a cohort of IDF elite soldiers during their first year of training and headquarter soldiers from the same base.

Methods: An antigen microarray, spotted with recombinant glycoproteins and whole inactivated viruses of common upper respiratory tract infections, was used to profile antibodies in serum and saliva samples collected from two groups of soldiers: (1) combat soldiers from an IDF elite unit during their first year of training (recruits; n=51), and (2) support staff from the unit’s headquarters (n=34). In both groups some of the soldiers were vaccinated with the seasonal influenza vaccine a few months before the trial began. Our microarrays included antigens of 54 influenza strains, to compare the response to vaccination in the groups. Serum and saliva samples were collected from each soldier at four different time points over a period of 15 months (T1-T4).

Results: Among the unvaccinated recruits, a significant increase in the median magnitude of anti-influenza antibodies at T2 suggested influenza infections in this group. Such increase in the median levels of anti-influenza antibodies was not observed in the vaccinated recruits or in support soldiers.

We also found that CMV seropositivity was associated with development of higher levels of IgG antibodies to whole influenza viruses but lower levels of IgG to recombinant influenza hemagglutinin (HA) proteins following influenza vaccination.

Discussion and conclusions: These findings suggest that vaccination of recruits is important for preventing influenza infections. In addition, CMV infection may affect not only the level but also the repertoire of antibodies developed following influenza vaccination.