Variability of the immune response in freshwater sponges

Abstract

AbstractThe variability of the immune response of four species of freshwater sponges, common in Belgium, Ephydatia fluviatilis, Ephydatia mulleri, Spongilla lacustris, and Eunapius fragilis, has been analyzed at the cellular level.For each species, strains, which are the collection of all the sponge individuals able to fuse compatibly their aquiferous system, were collected in natural ponds and isolated.In most cases, the general immune response corresponds to a three‐step process restricted to the zone of contact. This process includes: the fusion of the sponges coming into contact, a local cell accumulation, and the separation of the alien sponges.The variability of the immune reaction mainly concerns the existence and the duration of the fusion step and the possible secretion of a collagen barrier between the separated alien sponges. In contrast, for all the combinations studied, the accumulated cells differentiate and organize themselves in two facing layers of pinacocytes.In some allocombinations, involving S. lacustris strain δ, a general reaction was recorded. In these pairings, after the initial fusion, the alien sponges undergo a temporary involution followed by the segregation and reconstitution of two separated functional sponges.Our exhaustive analysis leads to the conclusion that the alloimmune responses vary according to the species and even within a single species, according to the strains paired. In contrast, all the xenocombinations undergo a similar process consisting in the direct and complete separation of the sponges.These results demonstrate the possibility for freshwater sponges to diversify their responses to nonself and consequently to discriminate between different nonself.