In vitro and in vivo studies of ribavirin action on Brazilian Orthobunyavirus.

Oropouche, Caraparu, Guama, Guaroa, and Tacaiuma are viruses (genus Orthobunyavirus) that cause human febrile illnesses and encephalitis. The goal of this study was to evaluate the antiviral action of ribavirin on these orthobunyaviruses to achieve a therapeutical agent to treat the diseases caused by these viruses. In vitro results showed that ribavirin (50 microg/mL) had antiviral activity only on the Tacaiuma virus. Addition of guanosine in the culture reversed the antiviral effect of ribavirin on Tacaiuma virus, suggesting that ribavirin inhibited this virus by reducing the intra-cellular guanosine pool. Moreover, ribavirin was not an effective drug in vivo because it was unable to inhibit the death of the mice or virus replication in the brain. The results suggest that ribavirin has no antiviral activity on the Oropouche, Caraparu, Guama, Guaroa, or Tacaiuma viruses; consequently, ribavirin would not be a good therapeutical agent to treat these arboviruses.

Chemokine production and leukocyte recruitment to the lungs of Paracoccidioides brasiliensis-infected mice is modulated by interferon-gamma.

Chemokines and chemokine receptors play a role in cell recruitment during granulomatous inflammatory reactions. Here, we evaluated the expression of chemokines and chemokine receptors and their regulation by IFN-gamma in the course of Paracoccidioides brasiliensis (Pb) infection in mice. We found an association between KC and MIP-1alpha (CCL3) production and neutrophil infiltration in the lungs of Pb-infected mice during the early acute phase of infection. High levels of RANTES/CCL5, MCP-1/CCL2, IP-10/CXCL10, and Mig/CXCL9 simultaneously with mononuclear cell infiltration in the lungs was found. In the absence of IFN-gamma (GKO mice) we observed increased production of KC and MIP-1alpha and chronic neutrophilia. Moreover, we found a change in the chemokine receptor profiles expressed by wild-type (WT) versus GKO animals. Increased expression of CXCR3 and CCR5, and low levels of CCR3 and CCR4 were observed in the lungs of Pb-infected WT mice, whereas the opposite effect was observed in the lungs of GKO mice. Consistent with these results, infected cells from WT mice preferentially migrated in response to IP-10 (CXCR3 ligand), while those from GKO mice migrated in response to eotaxin/CCL11 (CCR3 ligand). These results suggest that IFN-gamma modulates the expression of chemokines and chemokine receptors as well as the kind of cells that infiltrate the lungs of Pb-infected mice.

Fas-Fas ligand (CD95-CD95L) and cytotoxic T lymphocyte antigen-4 engagement mediate T cell unresponsiveness in patients with paracoccidioidomycosis.

The mechanism that leads to the remarkable T cell unresponsiveness to antigens in paracoccidioidomycosis is unknown. We investigated the involvement of cytokines, of Fas-Fas ligand (Fas-FasL)-induced apoptosis, and of cytotoxic T lymphocyte antigen 4 (CTLA-4) engagement, in the mediation of this phenomenon. T cell unresponsiveness was not associated with imbalanced cytokine production or with absence of CD28 expression. Only patient T cells expressed higher levels of CTLA-4, Annexin V(+), and FasL. The addition of anti-FasL decreased the levels of apoptosis, suggesting an activation-induced cell death triggered through the Fas-FasL pathway. Blockage of CTLA-4 and FasL resulted in increased production of interferon-gamma. Moreover, concomitant inhibition of FasL and of CTLA-4, but not of transforming growth factor-beta, resulted in significant T cell proliferation in patients, in response to phytohemagglutinin. Together, these data show that apoptosis mediated by Fas-FasL and engagement of CTLA-4 are involved in modulation of the immune response in patients infected with Paracoccidioides brasiliensis.