Pertussis specific cell-mediated immune responses ten years after acellular pertussis booster vaccination in young adults.

ABSTRACT

BACKGROUND: One of the reasons for pertussis resurgence is waning immunity. Both humoral and cell mediated immunity (CMI) are essential for protection. The aim of this study was to evaluate CMI responses after acellular pertussis vaccination in young adults. METHODS: Fifty-seven young adults were followed for ten years after a diphtheria-tetanus acellular pertussis (dTpa) booster vaccination. A second booster was administrated at year 10. CMI was determined from peripheral blood mononuclear cells (PBMC) stimulated with vaccine antigens pertussis toxin (PT), filamentous hemagglutinin (FHA) and pertactin (PRN) before and one month after the second vaccination, using proliferation and IFN-γ and IL-17 ELISpot. In addition, the response to ten selected cytokines was measured from 14 subjects. RESULTS: Before the booster dose, positive proliferation was recognized in 51%, 53% and 89% of the subjects against PT, PRN and FHA, respectively. One month after, the positivity rate increased to 81%, 81% and 96%. Although the number of IFN-γ and IL-17 secreting cells was increased, the expression of most of the tested cytokines was found to be downregulated. After PT stimulation, only one (7.1%) subject had increased production in all cytokines, whereas six (42.9%) had decreased production of all cytokines. Ten subjects (71.4%) had decreased concentration of IFN-γ, the cytokine important for pertussis protection. CONCLUSIONS: CMI persists even when antibodies have decayed, and acellular pertussis vaccine enhances the CMI response. Further studies are needed to illustrate what factors cause the low production of some important cytokines.