Concomitant immunity
Concomitant immunity is the phenomenon where an individual with a persistent infection displays immunity to re-infections caused by similar pathogens. In other words, the persistence of the primary infection prevents the occurrence of secondary infections. The presence of concomitant immunity depends on the nature of the immune response caused by a latent infection and hence differs from pathogen to pathogen. The concept was originally developed in tumor immunology, where a mouse with a tumor graft does not allow a second tumor graft of the same type to develop. It has also been called premunition, nonsterilizing immunity, and infection-immunity. Being dependent on an existing infection, it is a type of acquired immunity.
| Pathogen | Mechanism |
| Lymphocytic choriomeningitis virus | "relatively long-lived" effector-like memory T cells at nonlymphoid sites |
| Leishmania major | "relatively short-lived" CD4+ regulatory T cells and CD4+ effector T cells |
| Onchocerca volvulus | Unclear, known to occur based on cytokine and antibody evidence |
| Schistosoma | Unclear, proposed to display concomitant immunity |
| Mycobacterium tuberculosis | tissue-resident Memory T cells with an estimated lifespan of 2-3 years |