In vivo and in vitro studies using larval and adult antigens from Neobenedenia melleni on immune response in yellowtail (Seriola lalandi).

Neobenedenia melleni is a monogenean parasite that causes significant mortality and economic losses in fish aquaculture. Changes in the antigenic composition of this parasite occur during its developmental stages. In this study, we evaluated humoral parameters in serum and transcriptional immune responses of yellowtail naturally infected with N. melleni. In addition, in vitro assays were performed to study the stimulatory effects of antigens from larvae and adults on spleen leucocytes from non-infected fish at 6 and 24 h post-stimulation. The results showed enhanced total protein, myeloperoxidase and antiprotease activities in N. melleni-infected fish compared with non-infected ones. The induction of Toll-like receptors (TLRs) and pro-inflammatory cytokines in spleen leucocytes during natural infection with N. melleni suggests that these immune-related genes play an important role in the initiation of the immune defence mechanism for controlling parasite infection. Interestingly, the magnitude of in vitro responses of spleen leucocytes was dependent on the parasitic stage. An important stimulation of gene expression by adult antigens on spleen leucocytes was observed. Differential expression patterns of TLRs and target cytokines in yellowtail leucocytes in both in vivo and in vitro studies suggest that the quality of yellowtail immune response is conditioned by N. melleni development.

The eosinophils in parasitic infections

Local and peripheal eosinophilia is a common feature of many helminth infections that present large, non-phagocytable surfaces to the inmune system. The effect of the eosinophils on these organisms has been studied in the last 18 years using schistosoma mansoni, trichinella spiralis, and other helminths as models. The early infection causes a nonspecific inflammation rich in macrophages, lymphocytes and neutrophils that sets the stage for a subsequent inmune response. The predominant effector elements of the inmune response are anaphylactic antibodies, mast cells, and eosinophils. Mast cell products attract eosinophils and concentrate antibodies and complement-covered parasites by their Fc and/or C3c receptors and release oxygen radicals and/or preformed proteins on the helmith surface. The radicals alter molecules of the parasite and the proteins disrupt its tegument or cuticle. Occasionally, they may harm host cells. Eosinophils also phagocytize and harm extracellular trypanosoma cruzi and may play a role in the damage to the host heart tissue. The eosinophil response is regulated by eosinophilopoietic factors (interleukines [IL] 3 and 5, and granulocyte macrophage colony-stimulating factor) eosinophilotactic factors (C5a from complement, eosinophil chemotactic factor of anaphylaxis [ECF-A], histamine, platelet stimulating factor, and other ECFs from mast cells and basophils, and ECF from parasites), and eosinophiloactivating factors (IL-5 from Th2 lymphocytes, tumor necrosis factor from macrophages, antibodies, and complement components). Other phagocytic cells (macrophages and neutrophils) also exhibit important anti-helminthic activities

Schikhobalotrema solitaria sp. n. and S. acanthuri Yamaguti, 1970 (Haplosplanchnidae: Digenea) in Brazilian marine fishes

Schikhobalotrema solitaria sp. n. is described from Stephanolepis hispidus (Linnaeus, 1758), and is characterized by the relation between oral sucker and pharynx 1:1,1. This Relation in the other species ranges between 1:0.3-0.6. It is more similar to S. manteri Siddiqi & Cable, 1960 in the distribution of vitellaria, differing from it in the size of vitelline follicles, extension of uterus and in the size of the eggs. S. acanthuri Yamaguti, 1970 is referred for the first time in South America in Mugil liza Valenciennes, 1836 representing a new host record.