Immunityagainst parasites may not be always bright Goswami Tapas* Department of Veterinary Microbiology, Institute of Veterinary Science and Animal Husbandry, Siksha ‘O’ Anusandhan (Deemed to be University), Bhubaneswar-751030, Odisha, India *Corresponding author E-mail id: goswami.tapas@gmail.com
Online published on 29 August, 2023. Abstract Metazoan parasites are common causative agents for a wide variety of infectious diseases of medical and veterinary importance. Parasites are known to be prime manipulators of the host immune system, concurrently, the immunity developed against parasites is relatively slow and often feeble to disrupt their lifecycle. Unlike PAMPs (pathogenassociated molecular patterns) expressed on microbes that activate TLRs, nematode-associated molecular patterns are not as specific to induce a strong innate immune response. Carbohydrate (CH) determinants present in helminth parasites are the prime targets for innate recognition by mammalian hosts. Very often, these carbohydrate moieties are equally expressed in host cells, therefore not too specific to be a distinguishing marker for parasites. The role of TLRs in nematode resistance is under controversy. Immunoglobulin switching from IgG to IgE during parasitic infection is well established; however, its protective role has not been verified. In contrast to bacteria and viruses, parasites are quite adept at hiding from the host immune system to avoid recognition as notorious invaders. Parasites can evade the immune system and reside within the host with long-term associations. During the completion of their lifecycle, they can quickly change the immunological signature molecule on their surface, an amazing power of camouflage to deceive the immune system. Habitually, nematode parasites induce a Th2 type of immune response essential for the expulsion of multicellular invaders. However, the magnitude of the response is not robust enough for pathogen elimination. The polarization of macrophages from M1 to M2, where M1 initiates the killing of the invader and M2 supports the healing of damaged tissue caused by the tissue-migrating juvenile form of the parasite, is a characteristic feature of type 2 immune response. The cumulative effect of antibodies, complement, and cell-mediated immune responses act synergistically to reduce the parasite burden. Nevertheless, the immunosuppressive environment created by the parasite due to the activation of Treg cells, supplemented with immunosuppressive cytokines produced by the host, provides survival advantages for the parasites. Experimental reports generated from several scientific labs indicate the possibility of generating vaccines against parasitic infections, yet the proof of concept has not appeared to be convincing for translational research. Vaccination against microbes has gained momentum, but limited success against extracellular parasites has been discussed further. Top Keywords Cytokines, Galectin, Macrophage, Parasite, Treg cells, Type 2 immunity. Top |