Serum Factor Inhibiting Leucocyte Migration in Nigerian School Children Infected with Schistosoma haematobium: A Possible Impediment to Vaccine Response

Abstract

Background: Schistosoma haematobium survives intravascularly for many years in the host through complex but poorly understood parasite adaptation and immune evasion mechanisms which could impair vaccine response. This study aimed to detect and partially characterise a serum factor in infected Nigerian schoolchildren that inhibits leucocyte migration, with potential implications for the efficacy of future schistosome vaccines. 

Materials and Methods: Leucocytes from fifteen urinary schistosomiasis (USS) patients and ten controls were stimulated for migration in the capillary tube using Schistosoma adult worm antigen (SAWA) with or without autologous or heterologous serum or SAWA eluates from Sephadex G200 column chromatography. The pooled eluate was partially characterised using standard methods.

Results: Percentage leucocyte migration index (%LMI) was significantly reduced in USS patients compared with the controls when SAWA or SAWA+USS serum was used to stimulate leucocyte migration. The %LMI of USS patients was significantly reduced in SAWA+autologous serum compared with SAWA+heterologous serum or SAWA alone. Eluates (in tubes 20 and 21) collected from column chromatography showed significantly reduced %LMI compared with eluates from other tubes, and was not affected by temperatures (-20⁰C to 56⁰C) or storage for up to 12 weeks. The molecular weight of pooled eluate was 108 kD. It moved at gamma-globulin band in electrophoresis, stained for glycoprotein, and was digested by papain or trypsin.

Conclusion: The unidentified serum factor that inhibited autologous leucocyte migration in patients with USS appears distinct from previously described factors. Adult Schistosoma may use this factor to evade host immune responses and may potentially impair the efficacy of schistosome vaccines.