Severe Natural Outbreak of Cryptocaryon irritans in Gilthead Seabream Produces Leukocyte Mobilization and Innate Immunity at the Gill Tissue

Abstract

The protozoan parasite Cryptocaryon irritans causes marine white spot disease in a wide range of fish hosts, including gilthead seabream, a very sensitive species with great economic importance in the Mediterranean area. Thus, we aimed to evaluate the immunity of gilthead seabream after a severe natural outbreak of C. irritans. Morphological alterations and immune cell appearance in the gills were studied by light microscopy and immunohistochemical staining. The expression of several immune-related genes in the gills and head kidney were studied by qPCR, including inflammatory and immune cell markers, antimicrobial peptides (AMP), and cell-mediated cytotoxicity (CMC) molecules. Serum humoral innate immune activities were also assayed. Fish mortality reached 100% 8 days after the appearance of the C. irritans episode. Gill filaments were engrossed and packed without any space between filaments and included parasites and large numbers of undifferentiated and immune cells, namely acidophilic granulocytes. Our data suggest leukocyte mobilization from the head kidney, while the gills show the up-regulated transcription of inflammatory, AMPs, and CMC-related molecules. Meanwhile, only serum bactericidal activity was increased upon infection. A potent local innate immune response in the gills, probably orchestrated by AMPs and CMC, is triggered by a severe natural outbreak of C. irritans.

Host responses against the fish parasitizing ciliate Cryptocaryon irritans

“…In addition, a similar phenomenon had been reported in yellowtail clownfish ( Amphiprion clarkii ) infected with C. irritans 24 . Non‐specific immunity provides the first line of defense against invading pathogens and it has been extensively studied 25 . C. irritans infection can induce a robust non‐specific immune responses for the ultimate survival of the infected host 26 .…”

“…A study of gilthead seabream (Sparus aurata L.) detected focal hemorrhages at the base of the scales and gill cover and aggregation of erythrocytes in the dermal layer after the invasion of C. irritans. 25 In addition, with the presence of C. irritans in gills of E. coioides, accumulated mast cells (MCs) were detected at the site of parasites infection. 33 In another report, in situ hybridization (ISH) showed that, 34 In addition, after C. irritans infection, the result of immunohistochemical staining (IHC) showed that acidophilic granulocytes are mobilized and their presence was increased in gill of gilthead seabream.…”

“…33 In another report, in situ hybridization (ISH) showed that, 34 In addition, after C. irritans infection, the result of immunohistochemical staining (IHC) showed that acidophilic granulocytes are mobilized and their presence was increased in gill of gilthead seabream. 25 Another report found that a large number of leucocytes, including neutrophil-like cells, eosinophilic granule cells, lymphocytes and monocytes, accumulated in the gills of orange-spotted grouper after they were infected by C. irritans. 32 Moreover, the expression changes of TCR co-receptors (EcCD3ε, EcCD4-1 and EcCD45), costimulatory molecules (EcCD83, EcCD80/86) and BCR signals (EcCD79s, EcIgM and EcIgT) from the C. irritans-infected E. coioides transcriptome were performed by real-time PCR.…”

“…24 Non-specific immunity provides the first line of defense against invading pathogens and it has been extensively studied. 25 C. irritans infection can induce a robust non-specific immune responses for the ultimate survival of the infected host. 26 The pro-inflammatory cytokine and chemokines produced by non-specific immune responses, will further activate the T and B cells-mediated specific immune responses to inhibit growth of parasites and mediate its clearance.…”

The relationship of neutrophil/lymphocyte ratio (NLR) and C-reactive protein (CRP) parameters with mortality in intensive care unit (ICU) patients

“…Especially, neutrophilic granulocytes are very effective in inflammatory reactions and the immune system. While the granulocytes are called innate immunity, leukocytes are termed in the acquired immune system [3].…”