Role of heterotypic T cell memory following influenza re-challenge and secondary bacterial infection

Abstract Following recovery from influenza infection, an immunological T cell memory compartment is established. Memory T cells are able to respond and react to conserved pieces of the virus providing heterotypic strain protection. The role that cellular memory plays in influenza re-challenge is a topic of ongoing interest. The potential to harness cellular immune memory, in particular tissue resident memory, could provide researchers with the means to develop a universal influenza vaccine able to elicit a powerful immune response that is poised and localized in the lung environment. Secondary bacterial infections in conjunction with influenza infection lead to increased instances of morbidity and mortality when compared to influenza infections alone. The role of heterotypic T cell memory and susceptibility to secondary bacterial pneumonias has yet to be elucidated. We hypothesize that prior exposure to influenza alters the memory response to a heterotypic super-infection re-challenge event. Mice were challenged with A/X-31(H3N2) and re-challenged 54 days later with strain A/PR/8/34 (H1N1), then challenged with MRSA on day 60. Sample analysis methods included histology, bacterial plating, flow cytometry, and RTPCR. Results suggest that mice with an established memory compartment are able to control secondary bacterial infections against MRSA as compared to their acute infected counterparts. Analysis of lung damage via histology also suggests that memory experienced mice are more protected from damage caused by secondary bacterial infection. This research suggests that the T cell memory compartment can limit the effects of bacterial super-infection in the context of heterotypic influenza strain challenge.