When T-helper cells don't help: immunopathology during concomitant infection

Immunological wrong turns in the face of multiple viral challenges

To further understand the myriad of ways by which viruses can cause disease, development of new and creative model systems using laboratory mice will be required. Mouse models have been essential tools for the study of viral pathogenesis over the past 50 years, allowing for detailed assessments of viral replication, spread and immune response induction. However, virtually all of these studies were accomplished using a single-challenge approach, in which immunologically naïve adult mice were inoculated with only one pathogen. This approach, while useful for exploring individual pathogen–host interactions, does not parallel the complexity of immune history and potential concurrent immune challenges that occur in humans. This review discusses current progress in viral pathogenesis using the single-challenge approach, followed by an overview of the present understanding of how concurrent immune challenges may influence pathogenesis. It is suggested that the development of more complex mouse models will be a substantial advance, leading to the discovery of previously unappreciated aspects of immune cell recruitment and novel ways by which viruses can, either directly or indirectly, promote illness.

Coinfection with Schistosoma mansoni is associated with decreased HIV-specific cytolysis and increased IL-10 production

Impaired virus-specific immune responses have previously been observed with Schistosoma mansoni coinfection. We characterized Gag-specific responses in HIV-1-positive Ugandans with and without S. mansoni coinfection. We observed no significant difference in the frequency of IFN-gamma CD8+ T cells between the two groups. Interestingly, expression of CD107, a marker for cytolytic activity, was significantly lower in volunteers with S. mansoni coinfection compared with those with HIV-1 infection alone (p = 0.002). In contrast, the frequency of IL-10-positive Gag-specific CD8+ T cell responses was higher in volunteers with S. mansoni coinfection (p = 0.004). Analysis of human CMV-specific CD8+ T cell responses in the same individuals failed to reveal a similar pattern of altered CD107 and IL-10 expression. Our results suggest that S. mansoni coinfection is associated with decreased Gag-specific CD8+ cytolytic T cell responses and increased number of Gag-specific IL-10 positive CD8+ T cells. Our findings may have important implications toward the implementation of HIV preventive and therapeutic programs in Africa.