DETECTION OF SPECIFIC AND CONSTITUTIVE ANTIBODY-SECRETING CELLS IN THE GILLS, HEAD KIDNEY AND PERIPHERAL-BLOOD LEUKOCYTES OF DAB (LIMANDA-LIMANDA)

The relative immunological importance of the gills of fish was investi gated in terms of antibody production by enumerating antibody secretin g cells (ASC) in the gills, head kidney and blood of dab (Limanda lima nda) using the ELISPOT assay. The contribution of 'constitutive' ASC i n the gill appeared more substantial than that of elicited specific AS C. The gills were found to contain a mean (+/-SD) of 4227 +/- 1029 'co nstitutive' ASC/10(6) cells which was fewer than the head kidney which contained a mean (+/-SD) of 15617 +/- 3723 'constitutive' ASC/10(6) c ells but more than peripheral blood leucocytes which contained a mean (+/- SD) of 2650 +/- 212 'constitutive' ASC/10(6) cells. The number of specific anti-human gamma globulin (HGG) ASC following parenteral or oral administration of HGG was also determined. Anti-HGG ASC were dete cted in all three tissues following parenteral immunization, peaking s imultaneously, 4 weeks post-immunization. The strongest response was f ound in the head kidney. After oral immunization, responses were much weaker; again the head kidney was the most active but the gill respons e was barely detectable. These data were complemented by measurement o f specific antibody in the serum by ELISA. Serum antibody titres follo wing immunization were found to correlate closely with the number of s pecific ASC in the head kidney following parenteral immunization where as serum antibody titres after oral administration of antigen most clo sely followed the number of specific ASC in the blood In the Light of these data it is suggested that the primary immunological role of the leucocytes in the gill may be in the earliest stages of defence agains t infection. (C) 1997 Elsevier Science B.V.