pathogens Review Human Mucosal IgA Immune Responses against Enterotoxigenic Escherichia coli Saman Riaz 1,2, Hans Steinsland 3,4 and Kurt Hanevik 1,5,* 1 Department of Clinical Science, University of Bergen, Jonas Lies veg 87, N-5021 Bergen, Norway;
[email protected] 2 Centre for International Health, Department of Global Public Health and Primary Care, University of Bergen, 5020 Bergen, Norway 3 Centre for Intervention Science in Maternal and Child Health, Centre for International Health, Department of Global Public Health and Primary Care, University of Bergen, 5020 Bergen, Norway;
[email protected] 4 Department of Biomedicine, University of Bergen, 5020 Bergen, Norway 5 Norwegian National Advisory Unit on Tropical Infectious Diseases, Department of Medicine, Haukeland University Hospital, 5021 Bergen, Norway * Correspondence:
[email protected]; Tel.: +47-5597-5000; Fax: +47-5597-2950 Received: 16 July 2020; Accepted: 24 August 2020; Published: 29 August 2020 Abstract: Infection with enterotoxigenic Escherichia coli (ETEC) is a major contributor to diarrheal illness in children in low- and middle-income countries and travelers to these areas. There is an ongoing effort to develop vaccines against ETEC, and the most reliable immune correlate of protection against ETEC is considered to be the small intestinal secretory IgA response that targets ETEC-specific virulence factors. Since isolating IgA from small intestinal mucosa is technically and ethically challenging, requiring the use of invasive medical procedures, several other indirect methods are used as a proxy for gauging the small intestinal IgA responses. In this review, we summarize the literature reporting on anti-ETEC human IgA responses observed in blood, activated lymphocyte assayss, intestinal lavage/duodenal aspirates, and saliva from human volunteers being experimentally infected with ETEC.