Although prolactin is well recognised as a cytokine, effects of hypoprolactinaemia on biological endpoints are not well described in humans. In-vitro and clinical studies suggest an influence on humoral and cell mediated immunity and autoimmunity. We studied basal and stimulated immune function in panhypopituitary adults with and without prolactin deficiency and age and gender matched healthy controls. The study was approved by hospital and local research ethics committees. Nine hypopituitary patients with prolactin deficiency (5 female, age 52.0±15.2 yrs; group 1), 12 matched hypopituitary subjects of normal prolactin status (4 female, age 46.5±13 yrs; group 2) and 12 matched volunteers (5 female, age 47.5±17.6 yrs; group 3) were studied. Baseline humoral immunity, pneumococcal titres (9 strains) 1 month after vaccination, T cell numbers and function using in-vitro response to gamma interferon and cross-sectional immunity to T cell dependent antigen tetanus toxoid were studied.
Absolute CD19+ cell numbers were reduced in group 1 (236.5±124) and elevated in group 2 (432.8±209.3), compared with group 3 (275±115), P=0.02. CD19+ correlated with prolactin level in the whole cohort (R=0.44, P=0.01). T cell numbers, immunoglobulins and T cell function were comparable between groups. Susceptibility for invasive pneumococcal infection one month after vaccination remained in 5 of 9 patients (55.6%) in groups 1 and 4 of 12 (33.3%) in group 2, compared with 100% immunogenicity in group 3, (P=0.01; comparison between groups 1&2 versus 3). Pattern of response (post versus pre- vaccination contrast in pneumococcal antibodies) was similar between groups with a proportionately attenuated response in groups 1 and 2. Immunity to tetanus toxoid was protective in all subjects (>0.01 IU/ml).
Abnormalities of humoral immune response are present in hypopituitary adults. CD19 expression appears to correlate positively with prolactin level, in keeping with previous data linking prolactin and autoimmunity. Panhypopituitarism is also associated with reduced response to pneumococcal vaccine.