The production of a 70 kDa heat shock protein by Toxoplasma gondii RH strain in immunocompromised mice

A 70 kDa heat shock protein (HSP70) has been reported previously to be stro ngly expressed in virulent Toxoplasma gondii strains taken from immunocompe tent mice but it is poorly expressed by virulent parasites in mice immunoco mpromised by treatment with cortisone acetate or by virulent parasites cult ured in vitro. Immune factors such as interferon-gamma, tumour necrosis fac tor and reactive nitrogen intermediates derived from nitric oxide are known to be important inducers of HSP70 production and are also known to be prod uced during the immune response to acute T. gondii infection. The ability o f these immune factors to induce T, gondii HSP70 production was tested by a nalysing HSP70 production in tachyzoites of the virulent RH strain of T. go ndii recovered from mice deficient in: (1) T cells (nude mice); (2) T and B cells (SCID mice); (3) interferon-gamma receptors (interferon-gamma recept or knockout mice). and (4) tumour necrosis factor receptors (tumour necrosi s factor receptor knockout mice). Parasites from nude and SCID mice produce d as much HSP70 as immunocompetent mice. Likewise, T. gondii tachyzoites fr om mice lacking receptors for interferon-gamma or tumour necrosis factor pr oduced HSP70 in quantities similar to wild-type mice. The ability to produc e reactive nitrogen intermediates in response to T. gondii infection, as de tected by elevated levels of nitrate and nitrite in sera, was normal in tum our necrosis factor receptor knockout mice but was completely lacking in in terferon-gamma receptor knockout mice, indicating that reactive nitrogen in termediates are also not responsible for induction of parasite HSP70. Thus, immune factors that induce HSP70 production in mammalian cells do not appe ar to play primary roles in inducing HSP70 production by T. gondii (C) 2000 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd . All rights reserved.