Divergent outcomes following transcytosis of IgG targeting intracellular and extracellular chlamydial antigens

Antibodies can play a protective but non-essential role in natural chlamydial infections dependent on antigen specificity and antibody isotype. IgG is the dominant antibody in both male and female reproductive tract mucosal secretions, and is bi-directionally trafficked across epithelia by the neonatal Fc receptor (FcRn). Using physiologically relevant pH-polarized epididymal epithelia grown on Transwells®, IgG specifically targeting an extracellular chlamydial antigen; the Major Outer Membrane Protein (MOMP), enhanced uptake and translocation of infection at pH 6-6.5 but not at neutral pH. This was dependent on FcRn expression. Conversely, FcRn-mediated transport of IgG targeting the intracellular chlamydial inclusion membrane protein A (IncA), induced aberrant inclusion morphology, recruited autophagic proteins independent of lysosomes, and significantly reduced infection. Challenge of female mice with MOMP-specific IgG-opsonized C. muridarum delayed infection clearance but exacerbated oviduct occlusion. In male mice, MOMP-IgG elicited by immunization afforded no protection against testicular chlamydial infection, whereas; the transcytosis of IncA-IgG significantly reduced testicular chlamydial burden. Together these data show that the protective and pathological effects of IgG are dependent on FcRn-mediated transport as well as the specificity of IgG for intracellular or extracellular antigens

Percentage weight change of animals following IN challenge with <i>C. muridarum</i>.

<p>Percentage weight change was calculated by comparing the pre-infection body weight to daily p.i body weights. The figure depicts the effect of vaccination with MOMP and (A) CT/CpG- or (B) CTA1-DD-based vaccines on weight loss following IN challenge infection. Unimmunized (primary infection), live infection (secondary infection) and no infection controls are also included. (C) Area under the curve (AUC) analysis of percentage weight change was the total area, of both negative and positive peaks in weight change, over the 10 day course of infection in arbitrary units. Results are presented as the mean ± SD. Significant differences were determined using a one-way ANOVA with Tukey’s post-test by comparing the weight changes between groups at the same point in time. One <i>P</i> value, the most significant, is given for groups showing a significant change. Significance was set at <i>P</i><0.05 for all tests. <i>P</i>>0.05 (not shown), 0.01–0.05 (*), 0.001–0.01 (**) and <0.001 (***).</p

Antigen-specific systemic antibodies in serum.

<p>(A) MOMP-specific serum IgG, IgA IgG1 and IgG2a following vaccination was quantified by direct ELISA. Endpoint tires were calculated for all samples using background absorbance of PBST plus two SD. The ratio of IgG2a:IgG1, used to determine Th1:Th2 polarization, is indicated above the titer bars in each group. (B) Percentage of infection neutralized <i>in vitro</i> was determined by incubation of <i>Chlamydia</i> with a 1/10 dilution of whole serum. Results are presented as the mean ± SD. Significant differences were determined using a one-way ANOVA with Tukey’s post-test. Significance was set at <i>P</i><0.05 for all tests. <i>P</i>>0.05 (not shown), 0.01–0.05 (*), 0.001–0.01 (**) and <0.001 (***).</p

Proliferation and cytokine production by lymphocytes isolated from the MdLN and stimulated with MOMP.

<p>Lymphocytes isolated from the MdLN draining the lungs were stimulated with MOMP or media for 72 hr. (A) Lymphocyte proliferation was determined by incubating the stimulated cells with thymidine for an additional 14 hr and expressed as stimulation index. (B) The amount of TNFα, IFNγ, IL-4, IL-10 and IL-17 (pg/mL) secreted by the lymphocytes were quantified using Bioplex<i>®</i> and ELISA. Results are presented as the mean ± SD. Significant differences were determined using a one-way ANOVA with Tukey’s post-test. Significance was set at <i>P</i><0.05 for all tests. <i>P</i>>0.05 (not shown), 0.01–0.05 (*), 0.001–0.01 (**) and <0.001 (***).</p

Proliferation and cytokine production by lymphocytes isolated from the spleen and stimulated with MOMP.

<p>Splenocytes were stimulated with MOMP or media for 72 hr. (A) Lymphocyte proliferation was determined by addition of thymidine for an additional 14 hr. Data are expressed as stimulation index (cpm of the MOMP stimulated cells divided by the cpm of media stimulated cells). (B) The amount of TNFα, IFNγ, IL-4, IL-10 and IL-17 (pg/mL) secreted by splenocytes following stimulation was quantified using Bioplex<i>®</i> and ELISA. Results are presented as the mean ± SD. Significant differences were determined using a one-way ANOVA with Tukey’s post-test. Significance was set at <i>P</i><0.05 for all tests. <i>P</i>>0.05 (not shown), 0.01–0.05 (*), 0.001–0.01 (**) and <0.001 (***).</p

Antigen-specific mucosal antibodies in BAL.

<p>(A) The induction of MOMP-specific IgG and IgA in the BAL following vaccination was quantified by direct ELISA. (B) Percentage of infection neutralized <i>in vitro</i> was determined by incubation of <i>Chlamydia</i> with a 1/10 dilution of BAL. Results are presented as the mean ± SD. Significant differences were determined using a one-way ANOVA with Tukey’s post-test. Significance was set at <i>P</i><0.05 for all tests. <i>P</i>>0.05 (not shown), 0.01–0.05 (*), 0.001–0.01 (**) and <0.001 (***).</p

The inflammatory conundrum - where exactly do we stand?

Schistosomiasis, caused mainly by S. mansoni, S. haematobium and S. japonicum, continues to be a serious tropical disease and public health problem resulting in an unacceptably high level of morbidity in countries where it is endemic. Praziquantel, the only drug currently available for treatment, is unable to kill developing schistosomes, it does not prevent re-infection and its continued extensive use may result in the future emergence of drug-resistant parasites. This scenario provides impetus for the development and deployment of anti-schistosome vaccines to be used as part of an integrated approach for the prevention, control and eventual elimination of schistosomiasis. This review considers the present status of candidate vaccines for schistosomiasis, and provides some insight on future vaccine discovery and design