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Evidence from epidemiological, clinical, and biological research resulted in the immune hypothesis: the hypothesis that immune system dysfunction is involved in the pathophysiology of schizophrenia spectrum disorders (SSD). The promising implication of this hypothesis is the potential to use existing immunomodulatory treatment for innovative interventions for SSD. Here, we provide a selective historical review of important discoveries that have shaped our understanding of immune dysfunction in SSD. We first explain the basic principles of immune dysfunction, after which we travel more than a century back in time. Starting our journey with neurosyphilis-associated psychosis in the nineteenth century, we continue by evaluating the role of infections and autoimmunity in SSD and findings from assessment of immune function using new techniques, such as cytokine levels, microglia density, neuroimaging, and gene expression. Drawing from these findings, we discuss anti-inflammatory interventions for SSD, and we conclude with a look into the future.

The course of infection, parasitic loads, and histopathology of cutaneous lesions, draining lymph node, spleen, and liver were compared in BALB/c and C57BL/6 mice over a period of 34 weeks after inoculation in footpad with promastigotes of a Leishmania mexicana reference strain. The results show that the primary footpad lesions first present a 12-week phase that develops similarly in both strains of mice. Thereafter, a cutaneous and visceral dissemination of L. mexicana parasites occurs in BALB/c mice; the latter experience an extensive breakdown of the lymphoid organ microarchitecture, whereas C57BL/6 mice succeed in eliminating the parasite infection from the lymph nodes but not from the primary cutaneous lesion, which does not heal. These results highlight marked differences between responses of key anatomical compartments controlling L. mexicana infection in BALB/c and C57BL/6 mice., Comparative Study, Journal Article, Research Support, Non-U.S. Gov't, info:eu-repo/semantics/published

The role of interleukin-12 (IL-12) has been clearly established in the resistance of C57BL/6 (B6) mice to Leishmania major infection, but its involvement in the control of Leishmania mexicana infection remains to be determined. Here, we show the following. (i) L. mexicana, in contrast to L. major, induces the development of nonhealing lesions in B6 mice. (ii) Cells expressing IL-12p40, gamma interferon (IFN-gamma), NOS2, and CD40L are numerous in the footpad lesion and/or the draining popliteal lymph node of animals infected for up to 14 weeks with L. mexicana. (iii) B6 mice, either IL-12p40 deficient or treated with IL-12p40-neutralizing antibodies, display a dramatic enhancement of primary and secondary lesions leading to death 10 weeks after inoculation with L. mexicana. (iv) Splenocytes harvested 4 and 8 weeks after infection of IL-12p40(-/-) B6 mice with L. mexicana are unable to produce IFN-gamma, but secrete IL-4, IL-10, and IL-18. Thus, the early control of L. mexicana infection by B6 mice is independent of IL-12, whereas IL-12 and Th1 responses play a key role in controlling the late stages of L. mexicana infection. However, they fail to resolve lesions, in contrast to L. major infection, emphasizing the different outcomes induced by these two Leishmania species in B6 mice., Comparative Study, Journal Article, Research Support, Non-U.S. Gov't, SCOPUS: ar.j, info:eu-repo/semantics/published

Although BALB/c mice develop lesions when infected with Leishmania mexicana, the mechanisms which are responsible for susceptibility to this parasite have not been elucidated. In contrast, susceptibility of BALB/c mice to Leishmania major has been shown to depend on the early production of interleukin-4 (IL-4) by T cells which react to the parasitic LACK antigen. Here, we demonstrate that the lesions induced by L. mexicana are delayed compared to those induced by L. major but rapidly develop at later time points. Interestingly, while LACK-tolerant BALB/c-derived IE-LACK transgenic mice were resistant to L. major, they were susceptible to L. mexicana and developed lesions similar to those observed in wild-type BALB/c mice. The latter result was observed despite the fact that (i) LACK was expressed by L. mexicana, (ii) splenocytes from BALB/c mice were able to stimulate LACK-specific T-cell hybridoma cells when incubated with live L. mexicana promastigotes, and (iii) LACK-specific T cells contributed to IL-4 production in L. mexicana-infected BALB/c mice. Thus, in contrast to what was observed for L. major-infected mice, LACK-specific T cells do not play a critical role in determining susceptibility to L. mexicana. Although BALB/c mice are susceptible to both L. major and L. mexicana, the mechanisms which are responsible for susceptibility to these parasites are likely to be different., Journal Article, Research Support, Non-U.S. Gov't, SCOPUS: ar.j, info:eu-repo/semantics/published