Tunicates and Immunology:

 

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One of the most exciting moments this semester (speaking of academia that is) was the moment I realized I could reference the same paper for both my Ecology of Atlantic Shores class and my Immunology class. As I read the article, relevant details about the immune system were being utilized in tunicate allorecognition research. My interest was sparked. I hope to relay some of this interesting information to others who, like me, are just beginning to learn about the immune system and/or ascidians. The following is just a taste of the amazing advances and studies that have been done with our far-off phylum friend, the tunicate.

            Ascidians are at a unique point in the phylogenetic tree. These small-sessile animals are protochordates; our most distant chordate cousins that lack a vertebrate. One might never guess the commonalities between humans and ascidians when you look at a picture of them. Yet, recent studies show a link between the two.

           
         All vertebrates have a specific immune system capable of an antibody response and recognition of non-self grafts, cells, or antigens. However, invertebrates lack these exclusive immune responses (Taneda, et al.  1985). This ability to tell self from non-self is called allorecognition, and has recently been found to exist in ascidians. Botryllus, an individual in the tunicata subphylum, has demonstrated recognition when one individual is placed next to another. If the two share a common FuHC allele, the tunicates will fuse, forming a single colony, and the stem cells of the healthiest individual will be inserted into the other organism (Stanford Alumni Association). The FuHC allele in compound ascidians is similar to the human MHC (major histocompatibility complex) which encodes proteins presented to them, thus targeting foreign molecules for eradication (Tomaso et al. 2005). If the two do not share a common FuHC allele, the colonies or individuals will reject each other, pulling away. These findings could be crucial in advances with rejection of grafts and transplant surgeries.