Thymic peptides, stress, and depressive symptoms in older men: A comparison of different statistical techniques for small samples

Thymic peptides play an important role in aging and immune regulation, but little is known about their relationship to psychosocial factors. One thymic fraction, thymosin-alpha 1 (TSN-alpha 1) may be of particular interest given its hypothesized role in the differentiation of immature T cells into functional, mature T cells. We examined the relationships among stress, psychological symptoms, and TSN-alpha 1 levels in two conditions; before and after a glucose challenge test. The sample consisted of 18 men, aged 48-80, participants in the Normative Aging Study. While none of the correlations reached significance in the baseline condition, life events and depressive symptoms were significantly correlated with TSN-alpha 1 in the postchallenge condition (r's = .57, and .62, respectively). Hierarchical regression analyses with cross-product interaction terms suggested that individuals who were high in both life events and depression showed the highest levels of postchallenge TSN-alpha 1, with the psychosocial variables accounting for 65% of the variance. Given the small sample size, we replicated these analyses using jackknife and bootstrap techniques, which generally confirmed these findings. Thus, these preliminary results suggest that psychosocial factors may be related to abnormal TSN-alpha 1 responses to a challenge.