Receptor-Mediated and Lectin-Like Activities of Carp (Cyprinus carpio) TNF-α

Abstract

Functional characterization of TNF-α in species other than mammalian vertebrates is limited, and TNF-α has been studied in a limited number of fish species, primarily in vitro using recombinant proteins. Studies on TNF-α from different fish species so far pointed to several inconsistencies, in particular with respect to some receptor-mediated activities of fish TNF-α, such as the ability to directly activate phagocytes. In the present study a comprehensive analysis of in vitro as well as in vivo biological activities of two isoforms of carp TNF-α was performed. Our results show that carp TNF-α directly primes carp phagocytes and indirectly promotes typical receptor-mediated activities such as phagocyte activation by acting via endothelial cells. Additionally, for the first time in nonmammalian vertebrate species, the lectin-like activity of fish TNF-α homologs was investigated. Our results show an evolutionary conservation of function of this receptor-independent activity of TNF-α not only in cyprinid fish, but also in perciform and salmonid fish. The role of TNF-α in vivo, during infections of carp with the blood parasite Trypanoplasma borreli, was examined using three fundamentally different but complementary approaches: (1) inhibition of TNF-α expression, (2) overexpression of TNF-α, and (3) inhibition of shedding of membrane-bound TNF-α. Our results show that, also in fish, a tight regulation of TNF-α expression is important, since depletion or excess of TNF-α can make an important difference to survival of infection. Finally, we demonstrate a crucial protective role for membrane-bound TNF-α, which has a yet unexploited function in fish.

Two Types of TNF-α Exist in Teleost Fish: Phylogeny, Expression, and Bioactivity Analysis of Type-II TNF-α3 in Rainbow Trout Oncorhynchus mykiss

“…In contrast to the notion that fish TNF-a cannot directly activate phagocytes (macrophages) (37,38), the trout macrophagelike RTS-11 cell line responded to rTNF-a3 stimulation. We confirmed our results by stimulating primary macrophages with rTNF-a3.…”

“…Roca et al (37) reported that sea bream TNF-a cannot upregulate the expression of IL-6 or TNF-a and has only minor effects on the expression of IL-1b, IL-8, and COX-2 that could have resulted from contamination with other cells in the primary macrophage cultures. The carp rTNF-a molecules also were not able to induce proinflammatory cytokine expression in macrophages/phagocytes (38). Indeed, it was suggested that fish TNF-a has no direct effect on macrophages and that the main proinflammatory effects are mediated through the activation of endothelial cells (37,38).…”

“…The carp rTNF-a molecules also were not able to induce proinflammatory cytokine expression in macrophages/phagocytes (38). Indeed, it was suggested that fish TNF-a has no direct effect on macrophages and that the main proinflammatory effects are mediated through the activation of endothelial cells (37,38). Such studies raise questions concerning the evolution of TNF-a function and, in particular, its role in the regulation of the inflammatory network in different vertebrate groups.…”

Direct involvement of tumor necrosis factor-α in the regulation of glucose uptake in rainbow trout muscle cells

“…Over the last few years, recombinant TNF-␣ proteins from several fish species have been produced, and their effects on immune cells and tissues have been investigated (23,24,26,28,36,38,39,45,47,49). However, there is no information available to date on the metabolic effects of homologous recombinant TNF-␣ in nonimmune cells or tissues from fish.…”

Innate immunity of carp : fishing for receptors

“…Although related, T. borreli and T. carassii induce fundamentally different immune responses in the carp host (reviewed in . For example, in T. borreli-infected carp, gene expression profiles show up-regulated expression of cytokines including ifnγ (Stolte et al, 2008) and tnfα (Forlenza et al, 2009). At the same time, inos gene expression is up-regulated in head kidney, spleen, PBL and liver leading to NO production and a dramatic increase in serum nitrite levels and tissue nitration (Forlenza et al, 2008b;Joerink et al, 2006;Saeij et al, 2000Saeij et al, , 2002.…”