Aging is a complex process that reduces immunity and subsequently increases susceptibility to and complications of infections in the elderly. The consequence is that 90% of influenza-related deaths in the United States occur in older adults. The goal of our research is to understand how age-related changes in the immune system impact the course of influenza infection. Some of the most critical changes occur in CD4+ T helper (Th) subsets, which develop multiple defects resulting in reduced humoral immunity to both infections and vaccinations. To better understand the effects of aging on the immune response in influenza infection, we examined CD4+ Th subsets in aged mice to assess function and phenotype. Influenza-specific Th subsets can be distinguished by expression of cell surface markers PSGL1 and Ly6C: PSGL1loLy6Clo are T follicular helper (Tfh)-like, PSGL1hiLy6Clo are memory-like and PSGL1hiLy6Chi are Th1 effectors. To further explore the phenotypic changes in the Th subsets, we examined gene expression via RT-PCR.
We examined four groups of mice: naïve and influenza infected young (9 wk) and naïve and influenza infected aged (12 mo). Both infected groups were given flu via intranasal infection. Spleens and lymph nodes were pooled from 5 individual mice on Day 0 and post-infection Day 7 for naïve and infected groups, respectively. Fluorescent activated cell sorting (FACS) was performed and gating strategies were used based on PSGL1 and Ly6C protein expression, creating the CD4+ Th cell subsets. RNA was transcribed to cDNA using a reverse transcriptase kit and used in RT-PCR to evaluate gene expression in the Th cell subsets, using preformed PCR arrays.
Th1 effectors (PSGL1hiLy6Chi) decreased and Tfh subsets (PSGL1loLy6Clo) increased with age in naïve and flu infected mice. Gene expression in the infected mice was correlated to Th1 response.
With aging, the Th1 effector subset decreases and the Tfh-like population is increased in both aged naïve and influenza infected mice. Gene expression in the infected mice had more of a propensity for CD4+ Th1 which is involved in defense to viruses. Comparison of young and aged Th subsets will help determine if changes in gene expression correlate with age-related differences in response to influenza infection.
T. T. Hypolite,
L. Haynes, None
L. M. Chirch, None