Neglected Biological Features in Cnidarians Self-Nonself Recognition

Abstract

Cnidarian taxa, currently of the most morphologically simplest extant metazoans, exhibit many salient properties of innate immunity that are shared by most Animalia. One hallmark constituent of immunity exhibit by most cnidarians is histocompatibility, marked by wide spectrum of allogeneic and xenogeneic effector arms, progressing into tissue fusions or inflammatory rejections. Scientific propensity on cnidarians immunity, while discussing historecognition as the ground for immunity in these organisms, concentrates on host-parasitic and disease oriented studies, or focuses on genome approaches that search for gene homologies with the vertebrates. Above tendency for mixing up between historecognition and host-parasitic/disease, highlights a serious obstacle for the progress in our understanding of cnidarian immunobiology. Here I critically overview four 'forgotten' cnidarian immune features, namely, specificity, immunological memory, allogeneic maturation and natural chimerism, presenting insights into perspectives that are prerequisite for any discussion on cnidarian evolution. It is evident that cnidarian historecognition embraces elements that the traditional field of vertebrate immunology has never encountered (i.e., variety of cytotoxic outcomes, different types of effector mechanisms, chimerism, etc.). Also, cnidarian immune features dictating that different individuals within the same species seem to respond differently to the same immunological challenge, is far from that recorded in the vertebrates' adaptive immunity. While above features may be connected to host-parasitic and disease phenomena and effector arms, they clearly attest to their unique critical roles in shaping cnidarians historecognition, calling for improved distinction between historecognition and host-response/ disease disciplines. The research on cnidarians immunity still suffers from the lack of accepted synthesis of what historecognition is or does. Mounting of an immune response against conspecifics or xenogeneic organisms should therefore be clearly demarcated from other paths of immunity, till cnidarian innate immunity as a whole is expounded.

Cancer across the tree of life: cooperation and cheating in multicellularity

“…In addition to the calicoblastic epitheliomas, necroses and abnormal growths can occur when two sufficiently different hydrocoral Millepora dichotoma individuals come in contact [ 117 ]. Furthermore, galls and other cancer-like growths can be generated in corals by infection with trematodes, fungi and green algae [ 115 ].…”

Stem Cells and Innate Immunity in Aquatic Invertebrates: Bridging Two Seemingly Disparate Disciplines for New Discoveries in Biology

“…Indeed, while no homology has been established between marine invertebrates and vertebrates allorecognition genes, and not even among those of different invertebrate species (47,(169)(170)(171), a wide range of marine invertebrates, including sponges, cnidarians, bryozoans, and ascidians, reveal allorecognition competencies that represent high specificity and accuracy (44,172,173), also reflecting highly conserved effector mechanisms for innate immunity in the animal kingdom (40,(42)(43)(44)46). The discovery of specific and complex non-transitive hierarchies in marine invertebrates (174)(175)(176) is dictated by a variety of effector mechanisms that are tailored to recognize different conspecifics (177).…”

“…Allorecognition in aquatic invertebrates has been probably developed for purposes such as the regulation of gametic compatibility (164,178), for the discriminatory machinery of within-organism conflicts (179), as a platform to purge nascent selfish cells (39), as a partisan tool following the completion of each major evolutionary transmission (180) and for protection against predatory cell lineages of the same species, part of the costs of fusion with non-self, where stem cell lineages play a major role (47,(181)(182)(183)(184). It is manifested by specificity, immune priming, allogeneic maturation and natural chimerism (176,(185)(186)(187)(188), many of them managed by stem cells. These allorecognition phenomena exhibit suites of effector mechanisms (specific and non-specific) that are based on extreme allotypic diversity, commonly emerged in wide groups of marine invertebrates, and are recurrently seen in nature in the wake of tissue contacts among conspecifics.…”

Morphometric and allometric rules of polyp's landscape in regular and chimeric coral colonies of the branching species Stylophora pistillata

“…However, due to the proximity of the two metamorphosed planulae, and spreading of the two young spat on the substrate, the tissues of the two came to contact, leading to allogeneic fusion (chimeras; Figure 2, Chimera) or rejection. 49…”