CD4 and parasitic infectious disease: Thus, although the differential effect of helminth infection on the CTB and LPS immune response suggests a possible CD4+ T-cell dependent mechanism, our IgG subclass studies suggest that the immunomodulatory effect of concomitant parasitic infection on the immune response to the mucosal pathogen V. cholerae does not fall easily into a classic Th1 or Th2 polarization of the immune response.