Infection of susceptible mice with the Colombiana strain of Trypanosoma cruzi results in an orchestrated expression of chemokines and chemokine receptors within the heart that coincides with parasite burden and cellular infiltration. CC chemokine receptor 5 (CCR5) is prominently expressed during both acute and chronic disease, suggesting a role in regulating leukocyte trafficking and accumulation within the heart following T. cruzi infection. To better understand the functional role of CCR5 and its ligands with regard to both host defense and/or disease, CCR5(-/-) mice were infected with T. cruzi, and the disease severity was evaluated. Infected CCR5(-/-) mice develop significantly higher levels of parasitemia (P < or = 0.05) and cardiac parasitism (P < or = 0.01) during acute infection that correlated with reduced survival. Further, we show that CCR5 is essential for directing the migration of macrophages and T cells to the heart early in acute infection with T. cruzi. In addition, data are provided demonstrating that CCR5 does not play an essential role in maintaining inflammation in the heart during chronic infection. Collectively, these studies clearly demonstrate that CCR5 contributes to the control of parasite replication and the development of a protective immune response during acute infection but does not ultimately participate in maintaining a chronic inflammatory response within the heart.

The CC chemokine ligand 2 (CCL2) and CC chemokine receptor 2 (CCR2) are expressed in the heart after infection with Trypanosoma cruzi, suggesting that they play an important role in host defense. Infection of CCR2-deficient (CCR2(-/-)) mice with T. cruzi resulted in increased cardiac parasitism, yet the severity of cardiac inflammation was not affected. In addition, expression of interferon- gamma and inducible NO synthase in the heart, which are associated with effective killing of trypomastigotes, was not affected in CCR2(-/-) mice. These observations reveal that CCR2 signaling plays a distinct role that is separate from that of influencing either chemotaxis or previously defined anti-trypomastigote mechanisms for the control of T. cruzi's replication in the heart.

The expression of chemokines within the heart during experimental infection of susceptible mice with the Colombiana strain of Trypanosoma cruzi was characterized in an attempt to determine a functional role for these molecules in both host defense and disease. Analysis of chemokine transcripts revealed that CXC chemokine ligand 9 (CXCL9) and CXCL10, as well as CC chemokine ligand 2 (CCL2) and CCL5, were prominently expressed during acute disease, whereas transcripts for CXCL9, CXCL10, and CCL5 remained elevated during chronic infection. Inflammatory macrophages present within the heart were the primary cellular source of these chemokines following T. cruzi infection. Peak chemokine expression levels coincided with increased gamma interferon expression and inflammation within the heart, suggesting a role for these molecules in both host defense and disease. Indeed, simultaneous treatment of T. cruzi-infected mice with neutralizing antibodies specific for CXCL9 and CXCL10 resulted in an increased parasite burden that was sustained out to 50 days p.i. Antibody targeting either CXCL10 or CCL5 did not change either T. cruzi burden within the heart nor attenuate the severity of cardiac inflammation at any time point examined, while targeting CXCL9 in combination with CXCL10 resulted in increased parasite burden. Collectively, these studies imply that CXCL9 and CXCL10 signaling enhances immune responses following parasite infection. However, antibody targeting of CXCL9 and CXCL10, or CXCL10 alone, or CCL5 alone does not directly modulate the inflammatory response within the heart, suggesting that other proinflammatory factors are able to regulate inflammation in this tissue in response to T. cruzi infection.

Intracerebral infection of mice with mouse hepatitis virus, a member of the Coronaviridae family, reproducibly results in an acute encephalomyelitis that progresses to a chronic demyelinating disease. The ensuing neuropathology during the chronic stage of disease is primarily immune mediated and similar to that of the human demyelinating disease multiple sclerosis. Secretion of chemokines within the CNS signals the infiltration of leukocytes, which results in destruction of white matter and neurological impairment. The CC chemokine ligand (CCL)5 is localized in white matter tracts undergoing demyelination, suggesting that this chemokine participates in the pathogenesis of disease by attracting inflammatory cells into the CNS. In this study, we administer a mAb directed against CCL5 to mice with established mouse hepatitis virus-induced demyelination and impaired motor skills. Anti-CCL5 treatment decreased T cell accumulation within the CNS based, in part, on viral Ag specificity, indicating the ability to differentially target select populations of T cells. In addition, administration of anti-CCL5 improved neurological function and significantly (p < or = 0.005) reduced the severity of demyelination and macrophage accumulation within the CNS. These results demonstrate that the severity of CNS disease can be reduced through the use of a neutralizing mAb directed against CCL5 in a viral model of demyelination.

How chemokines shape the immune response to viral infection of the central nervous system (CNS) has largely been considered within the context of recruitment and activation of antigen-specific lymphocytes. However, chemokines are expressed early following viral infection, suggesting an important role in coordinating innate immune responses. Herein, we evaluated the contributions of CXC chemokine ligand 10 (CXCL10) in promoting innate defense mechanisms following coronavirus infection of the CNS. Intracerebral infection of RAG1(-/-) mice with a recombinant CXCL10-expressing murine coronavirus (mouse hepatitis virus) resulted in protection from disease and increased survival that correlated with a significant increase in recruitment and activation of natural killer (NK) cells within the CNS. Accumulation of NK cells resulted in a reduction in viral titers that was dependent on gamma interferon secretion. These results indicate that CXCL10 expression plays a pivotal role in defense following coronavirus infection of the CNS by enhancing innate immune responses.