Cellular and Molecular Immune Response to Chikungunya Virus Infection

Chikungunya virus (CHIKV) is a re-emergent arthropod-borne virus (arbovirus) that causes a disease characterized primarily by fever, rash and severe persistent polyarthralgia. In the last decade, CHIKV has become a serious public health problem causing several outbreaks around the world. Despite the fact that CHIKV has been around since 1952, our knowledge about immunopathology, innate and adaptive immune response involved in this infectious disease is incomplete. In this review, we provide an updated summary of the current knowledge about immune response to CHIKV and about soluble immunological markers associated with the morbidity, prognosis and chronicity of this arbovirus disease. In addition, we discuss the progress in the research of new vaccines for preventing CHIKV infection and the use of monoclonal antibodies as a promising therapeutic strategy

IL-10^−/− mice develop a less severe PCM associated with increased cellular immunity that results in decreased mortality rates.

<p>(A) IL-10^−/− and WT mice were inoculated with 1×10⁶<i>P. brasiliensis</i> yeast cells by the i.t. route, and severity of infection was evaluated by determining fungal loads in the lungs, livers and spleens at five post-infection periods (2, 4, 8, 16 and 23 weeks). The bars depict means ± SEM of the numbers of log₁₀ CFU obtained from groups of 6 to 8 mice. The results are representative of 3 experiments. ** <i>p</i><0.01, and *** <i>p</i><0.001, compared with WT controls. (B) Survival of IL-10^−/− and WT control mice after i.t. infection with 1×10⁶<i>P. brasiliensis</i> yeast cells was determined for a period of 220 days. Results are representative of two independent experiments (n = 12; * <i>p</i><0.05). (C) DTH responses mounted by <i>P. brasiliensis</i> infected mice. Control and infected WT and IL-10^−/− mice were injected intrafootpad with soluble <i>P. brasiliensis</i> yeast antigen (5 µg in 25 µl PBS) 24 hours before measurement of the footpad response at weeks 4 and 8 after fungal infection. Results are representative of two independent experiments. The bars depict means ± SEM of footpad swelling (* <i>p</i><0.05; ** <i>p</i><0.01; n = 6–8 mice).</p

IL-10 inhibits the phagocytic and fungicidal abilities of macrophages.

<p>(A) Macrophages from WT and IL-10^−/− mice either treated with IFN-γ or left untreated were infected for 2 h with <i>P. brasiliensis</i> yeasts labeled with propidium iodide (1∶1, fungus∶macrophage ratio). Co-cultures were gently washed and macrophages were analyzed by flow cytometry. (B) For fungicidal assay, macrophages were infected with <i>P. brasiliensis</i> yeasts (1∶12.5, fungus∶macrophage ratio) during 2 h, washed, and further cultivated for 48 h at 37°C in 5% CO₂. Supernatants were removed, the monolayers were washed with distilled water to lyse macrophages, and 100 µl of cell homogenates were assayed for the presence of viable yeasts by a CFU assay (C) NO production was measured in culture supernatants by Griess reagent. Data are means ± SEM of three independent experiments with similar results (* <i>p</i><0.05, ** <i>p</i><0.01 and *** <i>p</i><0.001).</p

At late stages of infection, IL-10 deficiency leads to reduced production of pro- and anti-inflammatory cytokines in the lungs of <i>P. brasiliensis</i>-infected mice.

<p>Levels of cytokines in lung homogenates of IL-10^−/− and WT control mice were measured after i.t. infection with 10⁶ yeast cells. Lungs were disrupted at weeks 8 and 16 after infection, and supernatants were analyzed for cytokine content by using the BD CBA mouse Th1/Th2/Th17 cytokine kit. The bars depict means ± SEM of cytokine levels (6 to 8 animals per group). * <i>p</i><0.05; ** <i>p</i><0.01, compared with WT control.</p

IL-10 deficiency determines increased humoral immunity in early <i>P. brasiliensis</i> infection.

<p>Levels of total specific Ig (A) and fungus-specific isotypes (B) in the sera of IL-10^−/− and WT mice at weeks 2, 4, 8, and 16 after i.t. infection with 10⁶ yeast cells. Sera were assayed for total Ig, IgM, IgA, IgG1, IgG2a, IgG2b and IgG3 by using an isotype-specific ELISA as detailed in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0002512#s2" target="_blank"><i>Materials and Methods</i></a>. The bars depict means ± serum titers (6 to 8 mice per group). The results are representative of 3 experiments. ** <i>p</i><0.01; *** <i>p</i><0.001, compared with WT controls.</p

IL-10^−/− mice clear <i>P. brasiliensis</i> infection and develop mild pulmonary inflammatory reactions.

<p>Photomicrographs of lungs, livers and spleens from WT (A to F) and IL-10^−/− (G to L) mice at week 8 after infection with 1×10⁶<i>P. brasiliensis</i> yeast cells. Compared with IL-10^−/− mice, increased number of inflammatory cells and more severe lesions were detected in WT mice. For panels: A, C, E, G, I and K, HE-stained, magnification ×10; for B, D, F, H, J and L, Groccot-stained, magnification ×10. Morphometrical analysis (M) confirmed the more extensive areas occupied by the lung and liver lesions of WT mice (*** <i>p</i><0.001).</p