Mucosal and Systemic Immune Responses in Patients with Diarrhea Due to CS6-Expressing Enterotoxigenic Escherichia coli

Abstract

Colonization factor CS6 expressed by enterotoxigenic Escherichia coli (ETEC) is a nonfimbrial polymeric protein. A substantial proportion of ETEC strains isolated from patients in endemic settings and in people whotravel to regions where ETEC is endemic are ETEC strains expressing CS6, either alone or in combination with fimbrial colonization factor CS5 or CS4. However, relatively little is known about the natural immune responses elicited against CS6 expressed by ETEC strains causing disease. We studied patients who were hospitalized with diarrhea (n ‫؍‬ 46) caused by CS6-expressing ETEC (ETEC expressing CS6 or CS5 plus CS6) and had a disease spectrum ranging from severe dehydration (27%) to moderate or mild dehydration (73%). Using recombinant CS6 antigen, we found that more than 90% of the patients had mucosal immune responses to CS6 expressed as immunoglobulin (IgA) antibody-secreting cells (ASC) or antibody in lymphocyte supernatant (ALS) and that about 57% responded with CS6-specific IgA antibodies in feces. More than 80% of the patients showed IgA seroconversion to CS6. Significant increases in the levels of anti-CS6 antibodies of the IgG isotype were also observed in assays for ASC (75%), ALS (100%), and serum (70%). These studies demonstrated that patients hospitalized with the noninvasive enteric pathogen CS6-expressing ETEC responded with both mucosal and systemic antibodies against CS6. Studies are needed to determine if the anti-CS6 responses protect against reinfection and if protective levels of CS6 immunity are induced by vaccination.Enterotoxigenic Escherichia coli (ETEC) strains are noninvasive enteropathogens which colonize the small intestine by means of colonization factors (CFs) and are the single most common cause of bacterial diarrhea in children in developing countries, as well as in adults, including travelers (24, 41). After colonization, the bacteria cause watery diarrhea due to production of heat-stable toxin (ST) (6) and/or heat-labile enterotoxin (LT) (30). CFs are antigens that are known to provide protection against infection with ETEC expressing homologous CFs (7,15,32,34). Although ETEC can express more than 25 different CFs, 7 of these CFs are more prevalent than others (7). CS6 has been shown to promote binding of ETEC to rabbit and human enterocytes but not to cultured intestinal cells and other human-derived tissue (11). It is one of the most common CFs, and in some studies CS6 has been found to be present on more than 30% of the strains isolated from patients with ETEC diarrhea, as well as from military and civilian travelers to countries where ETEC is endemic (24,28,29,41,42). This nonfimbrial surface antigen is present either alone or in association with CS4 or CS5 on ETEC strains producing either ST or both enterotoxin types (7,24,42). Based on the high prevalence of CS6-positive ETEC, CS6 has been examined as a vaccine antigen and has been administered by different immunization routes, including the oral (5, 14, 32, 36), transcutaneous (9, 43), and intranasal routes (3...

Case Series Study of Traveler's Diarrhea in U.S. Military Personnel at Incirlik Air Base, Turkey

“…However, the maximum titers and response rates were quite low. In contrast, a recent publication of CS6 immune responses in Bangladeshi patients hospitalized with CS6 ETEC infections showed robust IgA and IgG titers (20). One fundamental difference between these two studies is the study populations.…”

Enumeration of Gut-Homing β7-Positive, Pathogen-Specific Antibody-Secreting Cells in Whole Blood from Enterotoxigenic Escherichia coli- and Vibrio cholerae-Infected Patients, Determined Using an Enzyme-Linked Immunosorbent Spot Assay Technique

“…Previous studies have also shown development of mucosal and systemic immune responses against CS6 in humans infected with ETEC strains expressing CS6, with or without CS4 or CS5 (45), and oral immunization of mice with inactivated E. coli overexpressing CS6 induces substantial immune responses against this antigen (46). Patients infected with CS6-expressing ETEC develop not only CS6-specific IgG and IgA ASCs and antibody responses but also memory B cell responses and highly avid anti-CS6 IgA and IgG antibodies after onset of diarrhea (17).…”

Salmonella enterica Serovar Typhi-Specific Immunoglobulin A Antibody Responses in Plasma and Antibody in Lymphocyte Supernatant Specimens in Bangladeshi Patients with Suspected Typhoid Fever

“…We assayed immunoglobulin A (IgA), IgG, and IgM isotype-specific antibody responses to LPS, WC, and MP by using ELISA. We coated microtiter plates (Nunc F; Nunc, Denmark) with 100 l of LPS (2.5 g/ml), WC (10 8 CFU/ml), and MP (2 g/ml for plasma and 10 g/ml for ALS) and blocked them with 1% bovine serum albumin in PBS (29,31). To detect antigen-specific responses, we added 100 l of dilutions of plasma in PBS-Tween 0.1% bovine serum albumin (1:25 for IgA and IgM and 1:50 for IgG isotypes) or 100 l (1:2 dilution for IgA) of ALS specimens to coated plates, which were then incubated for 90 min at 37°C.…”