Eosinophils, basophils and myeloid-derived suppressor cells in chronic Loa loa infection and its treatment in an endemic setting

• Published in: PLoS neglected tropical diseases 2024-05, Vol.18 (5), p.e0012203-e0012203
• Main Authors: Burger, Gerrit, Adamou, Rafiou, Kreuzmair, Ruth, Ndoumba, Wilfrid Ndzebe, Mbassi, Dorothea Ekoka, Mouima, Anne Marie Nkoma, Tabopda, Carole Mamgno, Adegnika, Roukoyath Moyoriola, More, Ayong, Okwu, Dearie Glory, Mbadinga, Lia-Betty Dimessa, Calle, Carlos Lamsfus, Veletzky, Luzia, Metzger, Wolfram Gottfried, Mordmüller, Benjamin, Ramharter, Michael, Mombo-Ngoma, Ghyslain, Adegnika, Ayola Akim, Zoleko-Manego, Rella, McCall, Matthew B B
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Albendazole; Albendazole - therapeutic use; Analysis; Animals; Basophils; Basophils - immunology; Biology and Life Sciences; Care and treatment; CD123 antigen; Cell activation; Chemokines; Chronic Disease; Chronic infection; Clinical trials; Cross-sectional studies; Cytokines; Endemic Diseases; Eosinophilia; Eosinophils; Eosinophils - immunology; Ethylenediaminetetraacetic acid; Female; Flow Cytometry; Gabon - epidemiology; Health aspects; Humans; Immunology; Immunomodulation; Infections; Inflammation; Leukocytes (basophilic); Leukocytes (eosinophilic); Loa - immunology; Loa - physiology; Loa loa; Loiasis - drug therapy; Loiasis - immunology; Malaria; Male; Medical research; Medical treatment; Medicine and Health Sciences; Medicine, Experimental; Microscopy; Middle Aged; Mortality; Myeloid-Derived Suppressor Cells - immunology; Parasites; Physiological aspects; Public health; Research and Analysis Methods; Roundworm infections; Signs and symptoms; Suppressor cells; Tropical diseases; Young Adult
• ISSN: 1935-2735; 1935-2727; 1935-2735
• DOI: 10.1371/journal.pntd.0012203

Chronic infection by Loa loa remains an unsolved immunological paradox. Despite harboring subcutaneously migrating adult worms and often high densities of microfilariae, most patients experience only relatively mild symptoms, yet microfilaricidal treatment can trigger life-threatening inflammation. Here, we investigated innate cell populations hypothesized to play a role in these two faces of the disease, in an endemic population in Gabon. We analyzed numbers and activation of eosinophils and basophils, as well as myeloid-derived suppressor cell (MDSC) subsets and associated circulating cytokine levels by flow cytometry in sex- and age-matched L. loa-uninfected (LL-), -amicrofilaraemic (MF-) and -microfilaraemic (MF+) individuals (n = 42), as well as microfilaraemic individuals treated with albendazole (n = 26). The percentage of eosinophils was lower in LL- (3.0%) than in the combined L. loa-infected population, but was similar in MF+ (13.1%) and MF- (12.3%). Upon treatment of MF+, eosinophilia increased from day 0 (17.2%) to day 14 (24.8%) and had decreased below baseline at day 168 (6.3%). Expression of the eosinophil activation marker CD123 followed the same pattern as the percentage of eosinophils, while the inverse was observed for CD193 and to some extent CD125. Circulating IL-5 levels after treatment followed the same pattern as eosinophil dynamics. Basophil numbers did not differ between infection states but increased after treatment of MF+. We did not observe differences in MDSC numbers between infection states or upon treatment. We demonstrate that both chronic infection and treatment of L. loa microfilaraemia are associated with eosinophil circulation and distinct phenotypical activation markers that might contribute to inflammatory pathways in this setting. In this first ever investigation into MDSC in L. loa infection, we found no evidence for their increased presence in chronic loiasis, suggesting that immunomodulation by L. loa is induced through other pathways.