Necator americanus infection: a possible cause of altered dendritic cell differentiation and eosinophil profile in chronically infected individuals.

BackgroundHookworms survive for several years (5 to 7 years) in the host lumen, inducing a robust but largely ineffective immune response. Among the most striking aspects of the immune response to hookworm (as with many other helminths) is the ablation of parasite-specific T cell proliferative response (hyporesponsiveness). While the role of the adaptive immune response in human helminth infection has been well investigated, the role of the innate immune responses (e.g., dendritic cells and eosinophils) has received less attention and remains to be clearly elucidated.Methodology/principal findingsWe report on the differentiation/maturation of host dendritic cells in vitro and the eosinophil activation/function associated with human hookworm infection. Mature DCs (mDCs) from Necator americanus (Necator)-infected individuals showed an impaired differentiation process compared to the mDCs of non-infected individuals, as evidenced by the differential expression of CD11c and CD14. These same hookworm-infected individuals also presented significantly down-regulated expression of CD86, CD1a, HLA-ABC, and HLA-DR. The lower expression of co-stimulatory and antigen presentation molecules by hookworm-infected-derived mDCs was further evidenced by their reduced ability to induce cell proliferation. We also showed that this alternative DC differentiation is partially induced by excreted-secreted hookworm products. Conversely, eosinophils from the same individuals showed a highly activated status, with an upregulation of major cell surface markers. Antigen-pulsed eosinophils from N. americanus-infected individuals induced significant cell proliferation of autologous PBMCs, when compared to non-infected individuals.ConclusionChronic N. americanus infection alters the host's innate immune response, resulting in a possible modulation of the maturation process of DCs, a functional change that may diminish their ability for antigen presentation and thus contribute to the ablation of the parasite-specific T cell proliferative response. Interestingly, a concomitant upregulation of the major cell surface markers of eosinophils was observed in hookworm-infected individuals, indicative of antigen-specific immune responses, especially antigen presentation. We showed that in addition to the postulated role of the eosinophils as effector cells against helminth infection, activated cells may also be recruited to sites of inflammation and contribute to the immune response acting as antigen presenting cells

Expression of cell surface markers on monocyte-derived dendritic cells obtained from healthy non-exposed individuals (n = 5), differentiated in the presence of hookworm antigens.

<p>Expression of CD11c (A), CD14 (B), CD80 (C) and CD86 (D). Median intensity of fluorescence is indicated on y axis (arbitrary units). Statistical differences are indicated in each graph with the significant P values.</p

Expression of surface cell markers on eosinophils from <i>Necator</i>-infected (closed circle) and non-infected (open circle) individuals.

<p>Expression of antigen presentation/activation molecules (A), immunoglobulin receptors (B), integrin/memory markers (C) and accessory molecules/eotaxin receptor (D). Results are expressed in median intensity of fluorescence as indicated on y axis (arbitrary units). Statistically significant differences (P≤0.05) between <i>Necator</i>-infected and non-infected individuals were found for all cell surface markers tested with exception for CD89.</p

Description of the study population.

†<p>Intensity of infection was expressed by mean (range) of number of eggs per gram of feces.</p>††<p>Reference values for healthy adults (adapted from Elin, 2004 <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0000399#pntd.0000399-Zimpfer1" target="_blank">[51]</a>).</p>*<p>Statistically different from control group (P<0.05).</p

Mixed leukocyte response induced by co-culturing of dendritic cells and heterologous PBMCs.

<p>Results are expressed in counts per minute (CPM) and the bars represent the median for each group. Statistical difference is indicated with the significant P value.</p

Flow cytometric analysis of monocyte-derived dendritic cell surface markers.

<p>(A) Analysis of dendritic cell differentiation/maturation (CD11c and CD14) and (B) expression of IgG receptor (CD16, FcγRIII). (C) Expression of co-stimulatory molecules. (D) Expression of cell presentation molecules. Median intensity of fluorescence is indicated on x axis (arbitrary units). Statistical differences are indicated in each graph with the significant P values.</p

Cell proliferation response of autologous PBMCs after exposure with hookworm stimulated eosinophils from <i>Necator</i>-infected and non-infected individuals.

<p>Results are expressed as stimulation index and the bars represent the mean for each group. Statistical difference between both groups is indicated with the significant P value.</p