THE IMMUNE RESPONSE OF THE DOGFISH SCYLIORHINUS CANICULA L.

A number of aspects of the humoral and cellular immune responses of the common dogfish Scyliorhinus canicula L. were examined in order to define the immunological status of the animal in relation to its phylogenetic origins. The dogfish was shown to have the ability to produce specific antibody in response to a variety of soluble and particulate protein antigens. The existence of several non-specific defence mechanisms was demonstrated including a well established reticulo-endothelial system capable of rapidly clearing injected foreign material from the blood and also the bacteriolytic enzyme, lysozyme. Specific antibody from the fish had marked agglutinating properties which could be destroyed with reducing agents but which could not be demonstrated to form precipitin lines in agar gels. It could also fix complement. Isolation and characterisation of the antibody molecule showed it to have virtually neutral electrophoretic mobility, a molecular weight of approximately 800,000 daltons and a sedimentation coefficient of 18.6S. On reduction the molecule was shown to comprise heavy and light polypeptide chains with molecular weights of 76,000 and 18,000 daltons, respectively. On the basis of these findings the antibody was considered to be of the IgM class of immunoglobulin found in higher vertebrates. This was the only immunoglobulin found in the dogfish although an antigenically identical protein with a molecular weight of 160,000 daltons was also demonstrated and this was considered to be a monomeric form of an IgM pentamer. A survey of lymphoid tissues revealed that the fish had a well developed spleen. This organ was also shown to be directly involved in immunological reactions. Conversely, the thymus was poorly developed and involuted during an early stage in the life of the fish. Its immunological contribution was not determined. Two other tissues, the organ of Leydig and the epigonal tissue were found to comprise a high proportion of poorly differentiated lymphoid cells and these were considered to be similar to the stem cells of the bone marrow found in mammals. Ultrastructural examination of peripheral blood leucocytes showed that they comprised populations of cells analagous, to mammalian lymphocytes, plasma cells, granulocytes, and monocytes. Using a specific antiserum and an immunofluorescence technique, a high proportion of leucocytes were revealed to have immunoglobulin determinants on their surface. In a number of experiments to investigate cellular functions in vitro it was found that dogfish leucocytes could be stimulated by a variety of mitogenic substances but these results were insufficient to provide evidence for lymphocyte heterogeneity. Evidence that the dogfish was capable of weak recognition of histocompatibility antigens was provided in vitro by mixed lymphocyte cultures and in vivo by reaction to injected allogeneic leucocytes. Although several different techniques were used no evidence of immediate hypersensitivity reactions could be demonstrated. Delayed hypersensitivity was shown, however, by the leucocyte migration inhibition test and possibly by local skin reactions. The immunological relationship of the dogfish to an intestinal helminth parasite, Proleptus obtusus, was also investigated. The fish was found to be capable of producing antibody specific for the cuticle of the nematode. The parasite could also invoke several cellular reactions including the stimulation of leucocytes in vitro and delayed but not immediate hypersensitivity

Polymeric enteral diets as primary treatment of active Crohn's disease: a prospective steroid controlled trial.

Thirty two patients with active Crohn's disease were included in a controlled randomised trial to determine the efficacy and safety of polymeric enteral nutrition compared with steroids, to achieve and maintain clinical remission. The polymeric diet was administered through a fine bore nasogastric tube by continuous, pump assisted infusion (2800 (SEM 120) kcal/day). The steroid group received 1 mg/kg/day of prednisone. Both treatments were effective in inducing clinical remission: 15 of the 17 patients given steroids and 12 of the 15 patients assigned to the polymeric diet went into clinical remission (defined by a Van Hees index < 120) within four weeks of treatment. The percentage reduction of the Van Hees index was 34.8 (4.9)% for steroids and 32.3 (5)% for enteral nutrition (mean difference 2.5%; 95% CI--11.8% to +16.8%). Mean time elapsed to achieve remission was similar in both groups (2.0 (1) v 2.4 (1.2) weeks). Tolerance of the enteral diet was excellent. Four patients in the steroid group had mild complications attributable to this treatment. Ten patients (66.6%) in the steroid group and five (41.6%) in the enteral nutrition group relapsed within a year of discharge, but no differences were found in the cumulative probability of relapse during the follow up period. These results suggest that polymeric enteral nutrition is as safe and effective as steroids in inducing short term remission in active Crohn's disease