Excretory–secretory products of helminth parasites: effects on host immune responses

Abstract

SUMMARYParasitic helminths excrete or secrete (ES) a variety of molecules into their mammalian hosts. The effects of these ES products on the host's immune responses are reviewed. Investigations into the source of antigenic or immunoregulatory ES products have identified the cuticular and tegumental surfaces of some nematodes and trematodes respectively as being important sources of ES products; other ES molecules are released through specialized excretory or secretory organs. It is proposed that the active shedding of surface antigens may serve as an important source of parasite antigens available to the immune system in a form in which they can be taken up and processed by antigen-presenting dendritic cells, macro-phages and certain B cells for presentation to T helper cells. The ES products of nematodes, trematodes and cestodes contribute to immune evasion strategies of the parasites through mechanisms including shedding of surface-bound ligands and cells, alteration of lymphocyte, macrophage and granulocyte functions and modulation of complement and other host inflammatory responses. Immunopathology may be induced by ES products as in the development of granulomas around entrapped schistosome eggs. In some host – parasite systems ES antigens may induce host-protective immune responses and this source of protective antigens has been utilized in the successful vaccination against helminth infections, particularly against infection with trichurid nematodes and the metacestode stage of cestode parasites. The use of ES antigens in immunodiagnosis of helminth infection is also briefly discussed.

Preliminary analysis of Sm14 in distinct fractions of Schistosoma mansoni adult worm extract

“…Products released by worms as excretory/secretory antigens have been considered as important source of antigens capable of generating immune response in hosts (Maizels et al 1982, Lightowlers & Rickard 1988, Maizels & Selkirk 1988, Lightowlers 1996, Wilson & Coulson 1998, Maizels et al 1999.…”

“…However, molecules derived from the tegument or cuticle of helminths make a substantial contribution to the contents of excretory/secretory products of the parasite maintained in vitro, and are probably also released in vivo (Lightowlers & Rickard 1988). The active release of antigens from the surface of helminths should have a potentially significant impact on the immunobiology of the helminth-host relationship throught their potential triggering effect on the immune system of infected hosts (Kaushal et al 1982, Maizels et al 1982, Butterworth 1984, Lightowlers & Rickard 1988, Matsumoto et al 1988.…”

“…Subsequent testing in a wide range of parasitic infections has proven excretory/secretory proteins to be successful immunogens (Lightowlers & Rickard 1988). Natural immunity to gastro-intestinal nematodes will develop in older animals and, with continued exposure to infective larvae, the immunity is maintained.…”

“…Evidence for the release of surface antigens of Ancylostoma caninum and Toxocara canis is provided by the observation that antibody bound to the surface of these nematodes is shed rapidly in vitro (Lightowlers & Rickard 1988). Moreover, recombinant polypeptides belonging to the Ancylostoma secreted protein (ASP) family have shown promise for reducing hookworm burdens (50-80%) after A. caninum challenge infection in mice.…”

Influence of Worm Infection on Immunopathological Effect of Mycoplasma Capricolum Capripneumoniae Pathogen in Goats

“…In contrast, pathogenic micro-organisms typically trigger a type 1 immune response which results in elevation in IL-12, IL-23 and IFN gamma and IL-17 (Anthony et al, 2007). Helminth excretory-secretory products can directly influence antigen presentation suppressing differentiation of Th1 and Th17 cells that are pro-inflammatory to support the development of the generally anti-inflammatory Th2 and T regulatory cells (Hewitson et al, 2009;Lightowlers and Rickard 1988;White and Artavanis-Tsakonas, 2012). Through immune modulation, infections can increase host susceptibility to other parasites (Abu-Raddad et al, 2006), enhance the intensity of other pathogens infections and increase disease duration.…”