Immune Response to the Mumps Virus in Iranian Unvaccinated Young Adults

Although the first mumps vaccine was licensed more than 50 years ago, the vaccine was added to Iran's Expanded Program on Immunization in 2003. Therefore, the majority of Iranians born before 2003 are unvaccinated, and their immunity is the result of natural infection. In order to evaluate cellular responses against the mumps virus following natural infection, we investigated 90 Iranian unvaccinated adults aged 20-30 years. Mumps specific memory CD4+ and CD8+ proliferation and frequency of cytotoxic lymphocyte CD8+ CD107a were evaluated using flow cytometry. Our results showed that 33 subjects were seronegative, but 28 of them showed degranulation of CD8+ T lymphocytes and expression of CD 107a, as well as proliferation of CD4 and CD8 T cells, in response to mumps antigen stimulation. In all seropositive subjects, degranulation of cytotoxic T lymphocytes and proliferation of CD4+ and CD8+ T lymphocytes was detected. Proliferation of T cells and degranulation of CD8 T cells in seropositive subjects was higher than in seronegative subjects. We conclude that natural mumps infection and subclinical reinfection could induce good protection, but the severe complications associated with mumps infections suggest the need for mumps vaccination. Natural boosters because of the prevalence of the wild-type virus may help with maintenance of immunity in populations with high vaccine coverage.