Leishmaniasis Is a Useful Model for Demonstrating Differences in Host Responses

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The protozoan parasite Leishmania major provides a powerful and illustrative example of how host responses can differ between individuals. These differences can lead to either clearance of the parasite or fatality from the infection. Leish-mania is a protozoan that lives in the phagosomes of macrophages. Resistance to the infection correlates well with the production of IFN-y and the development of a TH1 response. Elegant studies in mice have demonstrated that strains that are resistant to Leishmania develop a TH1 response and produce IFN-y upon infection. Such strains of mice become highly susceptible to Leishmania-induced fatal ity if they lose either IFN-y or the IFN-y receptor, further underscoring the importance of IFN-y in containing the infection. A few strains of mice, such as BALB/c, are highly susceptible to Leishmania, and these animals frequently succumb to infection. These mice mount a TH2-type response to Leishmania infection; they produce high levels of IL-4 and essentially no IFN-y. Thus, one difference between an effective and an ineffective defense against the parasite is the development of a TH1 response or a TH2 response. Recent studies demonstrate that one difference between the resistant strains of mice and BALB/c is that a small restricted subset of BALB/c CD4+ T cells are capable of recognizing a particular epitope on L. major, and this subset produces high levels of IL-4 early in the response to the parasite. This skews the response toward a predominantly TH2 type. Understanding how these different T-helper responses affect the outcome of infection could provide a more rational approach to the design of effective treatments and successful vaccines for other pathogens.

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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