Circulating Gut-Homing (α 4 β 7 + ) Plasmablast Responses against Shigella Surface Protein Antigens among Hospitalized Patients with Diarrhea

Developing countries are burdened withShigella diarrhea. Understanding mucosal immune responses associated with naturalShigella infection is important to identify potential correlates of protection and, as such, to design effective vaccines. We performed a comparative analysis of circulating mucosal plasmablasts producing specific antibodies against highly conserved invasive plasmid antigens (IpaC, IpaD20, and IpaD120) and two recently identified surface protein antigens,p an-S higella s urfacep rotein antigen 1 (PSSP1) and PSSP2, common to all virulentShigella strains. We examined blood and stool specimens from 37 diarrheal patients admitted to the Infectious Diseases & Beliaghata General Hospital, Kolkata, India. The etiological agent of diarrhea was investigated in stool specimens by microbiological methods and real-time PCR. Gut-homing (α4 β7 + ) antibody-secreting cells (ASCs) were isolated from patient blood by means of combined magnetic cell sorting and two-color enzyme-linked immunosorbent spot (ELISPOT) assay. Overall, 57% (21 of 37) and 65% (24 of 37) of the patients were positive forShigella infection by microbiological and real-time PCR assays, respectively. The frequency of α4 β7 + IgG ASC responders against Ipas was higher than that observed against PSSP1 or PSSP2, regardless of theShigella serotype isolated from these patients. Thus, α4 β7 + ASC responses to Ipas may be considered an indirect marker ofShigella infection. The apparent weakness of ASC responses to PSSP1 is consistent with the lack of cross-protection induced by naturalShigella infection. The finding that ASC responses to IpaD develop in patients with recent-onset shigellosis indicates that such responses may not be protective or may wane too rapidly and/or be of insufficient magnitude.