The major subunit of the toxin-coregulated pilus TcpA induces mucosal and systemic immunoglobulin A immune responses in patients with cholera caused by Vibrio cholerae O1 and O139

Abstract

Diarrhea caused by Vibrio cholerae is known to give long-lasting protection against subsequent life-threatening illness. The serum vibriocidal antibody response has been well studied and has been shown to correlate with protection. However, this systemic antibody response may be a surrogate marker for mucosal immune responses to key colonization factors of this organism, such as the toxin-coregulated pilus (TCP) and other factors. Information regarding immune responses to TCP, particularly mucosal immune responses, is lacking, particularly for patients infected with the El Tor biotype of V. cholerae O1 or V. cholerae O139 since highly purified TcpA from these strains has not been available previously for use in immune assays. We studied the immune responses to El Tor TcpA in cholera patients in Bangladesh. Patients had substantial and significant increases in TcpA-specific antibody-secreting cells in the circulation on day 7 after the onset of illness, as well as similar mucosal responses as determined by an alternate technique, the assay for antibody in lymphocyte supernatant. Significant increases in antibodies to TcpA were also seen in sera and feces of patients on days 7 and 21 after the onset of infection. Overall, 93% of the patients showed a TcpA-specific response in at least one of the specimens compared with the results obtained on day 2 and with healthy controls. These results demonstrate that TcpA is immunogenic following natural V. cholerae infection and suggest that immune responses to this antigen should be evaluated for potential protection against subsequent life-threatening illness.

FIG. 1.

TcpA-specific IgA responses in ALS assays for patients with cholera due to V. cholerae O1 Ogawa (O1/Og), O1 Inaba (O1/In), or O139. The data points indicate individual values, and the bars indicate geometric means. Asterisks indicate statistically significant differences between the day 2 responses and the day 7 responses (one asterisk, P < 0.01 to 0.001; two asterisks, P < 0.001). Statistically significant differences between the responses of healthy controls and the responses of patients during convalescence are indicated by dots (one dot, P < 0.01 to P < 0.001; two dots, P < 0.001). mAB, milliabsorbance units; HC, healthy controls.

FIG. 2.

Immunoblot assay to detect TcpA-specific IgA antibodies in sera and fecal extracts. (A) Sera of patients infected with V. cholerae O1 Ogawa (lane 1), V. cholerae O1 Inaba (lane 2), and V. cholerae O139 (lane 3) and a healthy control (lane 4); (B) fecal extracts of patients infected with V. cholerae O1 Ogawa (lane 1), V. cholerae O1 Inaba (lane 2), and V. cholerae O139 (lane 3) and a healthy control (lane 4).