IL18 and pneumococcal meningitis: The pro-inflammatory mediator IL-1 consists of 4 molecular species (IL-1α, IL-1β, IL-1γ and IL-1δ) that exert similar biological activity through IL-1 receptor (IL-1R) type I. In vivo studies showed that IL-1R−/− mice, lacking an intact IL-1 signal, are more susceptible to develop pneumococcal meningitis, and that the disease is associated with higher mortality in IL-1R−/− mice compared to wild-type animals.