SPA-induced IL-2 secretion in cultures established 20 minutes (A) and 2 hours (B) post-intervention (PI). PBMC cultures were activated with SPA (10 μg/ml) at initiation and incubated at 37°C for 48 hr. The concentration of IL-2 (pg/ml) produced in vitro by cells from a subject at 20 min (A) and 2 hr (B) post intervention is plotted against the concentration of IL-2 produced at baseline by the same subject. Each point represents a subject for whom a complete set of data was available. Comparison of best fit lines revealed statistically significant differences between SMT-C (spinal manipulative therapy with cavitation, n = 26) and VC (venipuncture, n = 21) as well as SMT-NC (spinal manipulative therapy without cavitation, n = 23) and VC both for 20 min and 2 hr post intervention (see text for details).