Immunological Responses of the Dogfish (Scyliorhinus caniculaL.) to Cellular Antigens

Shark novel antigen receptors--the next generation of biologic therapeutics?

Over recent decades we have witnessed a revolution in health care as new classes of therapeutics based on natural biological molecules have become available to medical practitioners. These promised to target some of the most serious conditions that had previously evaded traditional small molecule drugs, such as cancers and to alleviate many of the concerns of patients and doctors alike regarding adverse side effects and impaired quality of life that are often associated with chemo-therapeutics. Many early 'biologics' were based on antibodies, Nature's answer to invading pathogens and malignancies, derived from rodents and in many ways failed to live up to expectations. Most of these issues were subsequently negated by technological advances that saw the introduction of human or "humanized' antibodies and have resulted in a number of commercial 'block-busters'. Today, most of the large pharmaceutical companies have product pipelines that include an increasing proportion of biologic as opposed to small molecule compounds. The limitations of antibodies or other large protein drugs are now being realized however and ever more inventive solutions are being sought to develop equally efficacious but smaller, more soluble, more stable and less costly alternatives to broaden the range of drug-able targets and therapeutic options. The aim of this chapter is to introduce the reader to one such novel approach that seeks to exploit a unique antibody-like protein evolved by ancestral sharks over 450 M years ago and that may lead to a host of new therapeutic opportunities and help us to tackle some of the pressing clinical demands of the 21 st century.

The development of primary and secondary lymphoid tissues in the nurse shark Ginglymostoma cirratum: B-cell zones precede dendritic cell immigration and T-cell zone formation during ontogeny of the spleen

Secondary lymphoid tissue and immunoglobulin (Ig) production in mammals is not fully developed at birth, requiring time postnatally to attain all features required for adaptive immune responses. The immune system of newborn sharks - the oldest vertebrate group having adaptive immunity - also displays immature characteristics such as low serum IgM concentration and high levels of IgM1gj, an innate-like Ig. Primary and secondary lymphoid tissues in sharks and other cartilaginous fish were identified previously, but their cellular organization was not examined in detail. In this study of nurse shark lymphoid tissue, we demonstrate that the adult spleen contains well-defined, highly vascularized white pulp (WP) areas, composed of a central T-cell zone containing a major histocompatibility complex (MHC) class II+ dendritic cell (DC) network and a small number of Ig+ secretory cells, surrounded by smaller zones of surface Ig+ (sIg+) B cells. In neonates, splenic WPs are exclusively B-cell zones containing sIgM+-MHC class IIlow B cells; thus compartmentalized areas with T cells and DCs, as well as surface Ig novel antigen receptor (sIgNAR)-expressing B cells are absent at birth. Not until the pups are 5 months old do these WP areas become adult-like; concomitantly, sIgNAR+ B cells are readily detectable, indicating that this Ig class requires a 'mature immune-responsive environment'. The epigonal organ is the major site of neonatal B lymphopoiesis, based on the presence of developing B cells and recombination-activating gene 1 (RAG1)/terminal deoxynucleotidyl transferase (TdT) expression, indicative of antigen receptor rearrangement; such expression persists into adult life, whereas the spleen has negligible lymphopoietic activity. In adults but not neonates, many secretory B cells reside in the epigonal organ, suggesting, like in mammals, that B cells home to this primary lymphoid tissue after activation in other areas of the body.

Development of the lymphomyeloid system in the dogfish, Scyliorhinus canicula

Previous studies on the morphology of the lymphomyeloid tissues in the dogfish, Scyliorhinus canicula, have been confined to adults. This study was restricted to the structure and functioning of the developing immune system in embryonic and post-hatch dogfish. A major feature of the developing immune system in S. canicula, is the succession of haemopoietic/lymphoid tissues. The liver is the first tissue to contain immunoglobulin positive cells at 2 months, followed by the interstitial kidney at 3 months. The thymus, spleen, and Leydig organ appears at 4 months while the epigonal and gut-associated lymphomyeloid tissues are the last tissues to differentiate. The haemopoietic/lymphoid nature of the kidney and thymus disappear at post-hatch and the other lymphomyeloid tissues persist through adult life. By the time of egg case splitting (ca. 6 months), when embryos receive massive exposure to water-borne antigens, the structural development of most of the lymphomyeloid tissues is well advanced.