Characterization of antibody responses to Wolbachia surface protein in humans with lymphatic filariasis

Abstract

Symbiotic Wolbachia organisms of filarial nematodes have received much attention as possible chemotherapy targets and disease-causing organisms. In order to further investigate the association between anti-Wolbachia immune responses and chronic filarial disease in humans, antibody responses to Wolbachia surface protein (WSP) were assayed in serum samples collected from 232 individuals living in Leogane, Haiti, an area where Wuchereria bancrofti infection is endemic, and from 67 North Americans with no history of lymphatic filariasis. As opposed to antifilarial antibody responses, which were largely influenced by the patient's infection status, the prevalence and levels of anti-WSP immunoglobulin G (IgG) antibodies among individuals with lymphedema or hydrocele were significantly greater than those in gender- and infection-matched individuals without disease. In at least one case, the anti-WSP IgG response was coincident with the onset of lymphedema development, and among anti-WSP-positive women with lymphedema, anti-WSP IgG levels were negatively correlated with the duration of lymphedema. The presence of anti-WSP IgG was also associated with the severity of inguinal adenopathy among men with hydrocele. In addition to the presence of anti-WSP antibodies among Haitians, 15 of 67 (22%) serum samples collected from individuals from North America, where filariasis is not endemic, were also positive for anti-WSP antibodies. In comparison to those from Haitians, anti-WSP antibodies from North Americans primarily recognized a distinct region of WSP located within the highly conserved second transmembrane domain. The results of this study demonstrate that anti-WSP antibody responses are associated with the presence of chronic filarial morbidity and not filarial infection status in humans and suggest that WSP should be further studied as a potential trigger for the development of filarial disease.

FIG. 1.

Composite graph showing a temporal association between anti-WSP IgG responses and the onset of lymphedema. Longitudinal serum samples were collected from a 54-year-old male before and after the onset of lymphedema. This individual was treated with diethylcarbamazine at week zero and developed unilateral lymphedema of the leg approximately 1 year posttreatment. Horizontal bars represent the period of time during which this individual was Ag⁺ Mf⁺ (black bar) and experienced lymphedema (gray bar). Line graphs represent anti-WSP IgG levels (squares), given in arbitrary units on the left axis, and antifilarial IgG1 (circles) and antifilarial IgG4 (triangles) levels, given in micrograms per milliliter on the right axis.

FIG.2.

Anti-WSP IgG levels are associated with the presence of lymphedema. Box and whisker plots show anti-WSP IgG (A), antifilarial IgG1 (B), and antifilarial IgG4 (C) antibody data from women in this study and North Americans. Horizontal lines represent the 25th, 50th, and 75th percentiles of anti-WSP IgG responses, given in arbitrary units, and antifilarial responses, given in micrograms per milliliter. Vertical lines represent the nonoutlier minimum and maximum responses for each group, and circles represent outliers.

FIG. 3.

Correlation between anti-WSP IgG levels and lymphedema duration among anti-WSP⁺ women with lymphedema. Correlation (r = 0.66) was determined by linear regression analysis.

FIG.4.

Anti-WSP IgG levels are associated with the presence of hydrocele. Box and whisker plots show anti-WSP (A), antifilarial IgG1 (B), and antifilarial IgG4 (C) antibody data from men in this study stratified by infection status. Individuals with hydrocele are shown on the left, and individuals without hydrocele are shown on the right. Horizontal lines represent the 25th, 50th, and 75th percentiles of anti-WSP IgG responses, given in arbitrary units, and antifilarial responses, given in micrograms per milliliter. Vertical lines represent the nonoutlier minimum and maximum responses for each group, and circles represent outliers.

FIG. 5.

Linear epitopes of WSP recognized by anti-WSP⁺ individuals with lymphedema (A) (n = 12) or hydrocele (B) (n = 16), asymptomatic Ag⁺ Mf⁺ individuals (C) (n = 8), asymptomatic Ag⁻ Mf⁻ individuals (D) (n = 7), and North Americans (E) (n = 9). Results are shown as the percentage of individuals recognizing at least one peptide who are positive for each of the 26 overlapping WSP peptides.