Many chiropractors share the belief that manipulative therapy can elicit viscerosomatic responses. Findings have suggested that manipulative therapy may affect blood pressure, hormone levels and the immune system. Furthermore, a growing body of evidence supports the idea that the immune system does not act independently, but is influenced by the nervous system. Early reports indicate that repeated spinal manipulation of subjects with neuromusculoskeletal disorders results in the elevation of circulating B-lymphocytes. Because of the suggested link between the nervous and immune systems, the present authors decided to monitor the ability of lymphocytes (T- and B-cells), which were isolated from asymptomatic subjects, to respond to mitogen stimulation following chiropractic upper cervical manipulation.
In a prospective, single-blind, randomized, controlled trial, the authors used laboratory findings to evaluate the possible effect of chiropractic cervical manipulation and sham treatment on the mitogenic response of lymphocytes found in peripheral blood. Four male and six female volunteers were obtained for the study by convenience sampling. All subjects were asymptomatic with respect to pain, but had to exhibit clinical evidence of upper cervical joint dysfunction. The subjects were randomly allocated to either the manipulation group or the sham group, the result being that seven subjects were in the manipulation group and three in the sham group. Subjects in the manipulation group received a high-velocity, low-amplitude chiropractic manipulation(s) at the level(s) of determined joint dysfunction, whereas the subjects in the sham group received a sham treatment(s) with a deactivated activator instrument at the level(s) adjacent to the determined segments of joint dysfunction. Peripheral blood was taken from each subject 15-20 min pre- and post-treatment. The degree of lymphocyte activation in each blood sample was measured with a mitogen response assay using phytohaemagglutinin (PHA) and pokeweed mitogen (PWM) as stimulators. The descriptive statistics suggested that the response of circulating lymphocytes in the manipulation group was lower after treatment. At the 0.5 and 1.0 microg mL (- 1) dilutions of PHA, this reduction was statistically significant. However, the sham group demonstrated marked increases in lymphocyte activation after treatment at all dilutions of PHA and PWM according to the descriptive statistics, with statistical significance at all PHA dilutions (but not for the PWM dilution). Post hoc Power analysis yielded a mixed set of results: the 95% confidence interval (CI) for the Power analysis was 19-61%. Based on this study, the suggested sample size for future studies should be at least 13 subjects per group (95% CI of four to 22 subjects). Generally, the effect-size calculations produced large to very large effect sizes (Cohen's d) for the majority of measures (>80%), with an overall 95% CI for effect size of 44-194%.
The present results suggest that an immediate, meaningful reduction in lymphocytic activation may occur after upper cervical chiropractic manipulation. These results support the hypothesis that chiropractic manipulation may affect the immune system. Since T- and B-cell activation is a component of the inflammatory response, the authors speculate that the reduction in the activation of these cells may contribute to the reduction of the inflammatory response often associated with common musculoskeletal disorders. Further robust studies with larger sample sizes are encouraged to verify the possible short- and long-term effects of manipulation on lymphocyte activation.