Scholarly record

HUMORAL IMMUNE RESPONSE OF HAEMOCYTES, RESPRESENTED BY NITRIC OXIDE AND PHENOL OXIDASE PRODUCTION

Hanan Al‐Khalaifah

Abstract

Molluscs are invertebrates that form one of the largest groups in the animal kingdom, with more than 100,000 known species. A wide range of molluscs including families of Pulmonata, Gastropoda, Planorbidae and Lymnaeidae are intermediate hosts of trematodes. The snail Lymnaea stagnalis belongs to the family Lymnaeidae under the order Basommatophora-class Pulmonata is known to be an intermediate host of several parasites such as Chaetogaster limnaei which belongs to the annelid family, Naididae, an ecologically diverse family of worms common in both running and standing waters. The length of the parasite ranges from 7 to 20 mm Chaetogaster limnaei parasite was found in all the 150 Lymnaea stagnalis snails that were collected during May, June and July. In common with other animals, snails have evolved an immune system that is capable of responding to non-self agents. The snail immune system plays an essential role in protecting from pathogens like parasites. The snail immune system is generally divided into two main arms: the adaptive (specific) and the innate (non-specific) immune responses. Components of the immune system include T-lymphocytes, B-lymphocytes, macrophages, natural killer cells, heterophils, basophils, diverse humoral communication factors such as eicosanoids and cytokines (e.g., interleukins, interferons, tumor necrosis factor) and effector molecules (e.g. immunoglobulins, complement, lysozymes, nitric oxide). Additionally, some tissues in the body are dedicated to support the immune system such as dendritic, reticular and stromal cells. Regulation and communication between various elements of the immune system result in highly organized interaction between the two main arms, resulting into birds possessing a highly sophisticated immune system, capable of protecting against invading pathogens. The complement system is considered to be an important element of the innate immune system that also triggers adaptive immunity. The complement system was capable of providing protection against parasites in the early innate defence in snails. Similar haemolytic complement activity was also reported against other agents. Like bacteria and viruses. Complement components are proteins and glycoproteins. Other cells such as tissue macrophages and blood monocytes are involved in complement production. These proteins are circulating in the blood in an inactive form. Once activated upon exposure to an antigen, they enter an enzymatic biochemical cascade that helps in the elimination of antigens by lysis of cells, opsonisation, binding to specific complement receptors on cells of immune system, and/or immune clearance of immune complexes. There are three different pathways by which the complement cascade is activated, namely the classical pathway, the alternative pathway and the mannan-binding lectin pathway. Snail's haemocyte monolayers were prepared to investigate effect of the parasite on some humoral immune response parameters such as: nitric oxide and phenol oxidase. The optimum period of time for production of nitric oxide and phenol oxidase was 6 hours post-exposure to live parasites, followed by dead parasites, and then parasite products. However, this response is insufficient to eliminate the parasite.

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