Comparison of immune responses to the O-specific polysaccharide and lipopolysaccharide of Vibrio cholerae O1 in Bangladeshi adult patients with cholera

Abstract

Immunity against Vibrio cholerae O1 is serogroup specific, and serogrouping is defined by the O-specific polysaccharide (OSP) part of lipopolysaccharide (LPS). Despite this, human immune responses to V. cholerae OSP have not previously been characterized. We assessed immune responses against V. cholerae OSP in adults with cholera caused by V. cholerae O1 El Tor serotype Inaba or Ogawa in Dhaka, Bangladesh, using O1 OSP-core-bovine serum albumin (OSPc:BSA) conjugates; responses targeted OSP in these conjugates. Responses of Inaba-infected patients to Inaba OSP and LPS increased significantly in IgG, IgM, and IgA isotypes from the acute to convalescent phases of illness, and the responses correlated well between OSP and LPS (R = 0.86, 0.73, and 0.91, respectively; P < 0.01). Plasma IgG, IgM, and IgA responses to Ogawa OSP and LPS in Ogawa-infected patients also correlated well with each other (R = 0.60, 0.60, and 0.92, respectively; P < 0.01). Plasma IgM responses to Inaba OSP and Ogawa OSP correlated with the respective serogroup-specific vibriocidal antibodies (R = 0.80 and 0.66, respectively; P < 0.001). Addition of either OSPc:BSA or LPS, but not BSA, to vibriocidal assays inhibited vibriocidal responses in a comparable and concentration-dependent manner. Mucosal IgA immune responses to OSP and LPS were also similar. Our study is the first to characterize anti-OSP immune responses in patients with cholera and suggests that responses targeting V. cholerae LPS, including vibriocidal responses that correlate with protection against cholera, predominantly target OSP. Induction of anti-OSP responses may be associated with protection against cholera, and our results may support the development of a vaccine targeting V. cholerae OSP.

Fig 1

Mean normalized IgG, IgM, and IgA responses in plasma of patients infected with V. cholerae O1 serotype Ogawa or Inaba to Inaba OSPc:BSA (OSP) and lipopolysaccharide (LPS). Plasma IgG, IgM, and IgA responses to Inaba OSP and LPS in Inaba-infected patients are shown in panels A, C, and E, and those in Ogawa-infected patients are shown in panels B, D, and F. Asterisks indicate a statistically significant difference (P ≤ 0.05) from baseline (day 2) levels within a particular antigen group.

Fig 2

Mean normalized IgG, IgM, and IgA responses in plasma of patients infected with V. cholerae O1 serotype Ogawa or Inaba to Ogawa OSPc:BSA (OSP) and lipopolysaccharide (LPS). Plasma IgG, IgM, and IgA responses to Ogawa OSP and LPS in Inaba-infected patients are shown in panels A, C, and E, and those in Ogawa-infected patients are shown in panels B, D, and F. Asterisks indicate a statistically significant difference (P ≤ 0.05) from baseline (day 2) levels within a particular antigen group.

Fig 3

Correlation between vibriocidal antibody responses and plasma IgG or IgM antibody responses to OSPc:BSA (OSP) and lipopolysaccharide (LPS). The lines indicate the correlations between the different responses to OSP and LPS and the vibriocidal antibody response.

Fig 4

Mucosal immune responses to Ogawa OSPc:BSA (OSP) and lipopolysaccharide (LPS). Asterisks indicate a statistically significant difference (P ≤ 0.05) from baseline (day 2). (A) Mean circulating antigen-specific IgG, IgM, and IgA ASC responses to Ogawa OSP, LPS, and CtxB with standard error bars. (B) ALS IgA responses to Ogawa OSP and LPS in healthy controls (HC) and Ogawa- and Inaba-infected patients. RF, responder frequencies.

Fig 5

Antigen-specific inhibition of vibriocidal antibody assays using OSPc:BSA (OSP) and lipopolysaccharide (LPS). Ag⁻ represents patient plasma not incubated with antigen. BSA and recombinant CtxB antigens were also assayed at concentrations of 1, 10, and 100 μg/ml, and no inhibition was detected. V. cholerae O1 Ogawa OSPc:BSA and Ogawa LPS were used for these experiments.