Abstract
Metazoan immunity is mainly associated with specialized cells that are directly involved with the immune response. Nevertheless, both in vertebrates and invertebrates other organs might respond to immune activation and participate either directly or indirectly in the ongoing immune process. However, most of what is known about invertebrate immunity has been restricted to immune effector cells and little information is available on the immune responses of other tissues or organs. We now focus on the immune reactions of the intestinal tissue of an echinoderm. Our study employs a non-conventional model, the echinoderm Holothuria glaberrima, to identify intestinal molecules expressed after an immune challenge presented by an intra-coelomic injection of lipopolysaccharides (LPS). The expression profiles of intestinal genes expressed differentially between LPS-injected animals and control sea water-injected animals were determined using a custom-made Agilent microarray with 7209 sea cucumber intestinal ESTs. Fifty (50) unique sequences were found to be differentially expressed in the intestine of LPS-treated sea cucumbers. Seven (7) of these sequences represented homologues of known proteins, while the remaining (43) had no significant similarity with any protein, EST or RNA database. The known sequences corresponded to cytoskeletal proteins (Actin and alpha-actinin), metabolic enzymes (GAPDH, Ahcy and Gnmt), metal ion transport/metabolism (major yolk protein) and defense/recognition (fibrinogen-like protein). The expression pattern of 11 genes was validated using semi-quantitative RT-PCR. Nine of these corroborated the microarray results and the remaining two showed a similar trend but without statistical significance. Our results show some of the molecular events by which the holothurian intestine responds to an immune challenge and provide important information to the study of the evolution of the immune response.
Highlights
In metazoans, the immune system is usually associated with specialized cells that are found distributed in the vascular system and within most tissues
Summary We have shown that a systemic injection of LPS in the sea cucumber H. glaberrima provokes changes in the expression of several intestinal transcripts
This expression profile seems to be organ-specific when compared to expression profiles of coelomocytes activated with LPS in both the holothurian or in the sea urchin
Summary
The immune system is usually associated with specialized cells that are found distributed in the vascular system and within most tissues. Human lymphocytes and invertebrate hemocytes/coelomocytes are examples of circulating cells specialized in immune defense. Certain organs are known to participate in immune responses. The human liver is associated with innate responses and its role as an immune organ is being increasingly investigated [1,2]. The kidney is an important immune organ where B-lymphocytes originate and differentiate [3] and in humans it is the subject of numerous studies on autoimmune disease and transplantation immunology [4,5]. The central nervous system is clearly affected by the immune state of the organism, playing a role in controlling body temperature and other immuno-modulatory responses [6,7]. In invertebrates, immune cells can be produced in definite lymphoid-like organs, i.e. the fat body of insects [8], but in some groups it has been shown that the immune function is shared or distributed by organs and tissues in different areas of the body (internal epithelia, gastric and excretory tissues)
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