Affinity maturation occurs in channel catfish (Ictalurus punctaus) following immunization with a T-cell dependent antigen

Long-Lived Plasma Cells Secrete High-Affinity Antibodies Responding to a T-Dependent Immunization in a Teleost Fish

“…The dynamics of antibody titers in supernatants mirrored that in the sera, increasing rapidly at the early response and peaking at week 8 (~500 units/mL), then decreasing slowly during the late response (Figure 5A). The antibody affinities in the supernatants were examined by the T1/T8 affinity ELISA, with the analysis of the ratio of TNP 1 -BSA to TNP 8 -BSA values (28, 35). In accordance with the kinetics of antibody affinity in the sera, supernatant antibody affinity increased rapidly at week 2 and was optimal at weeks 6–8 and was then maintained at a steady high level (Figure 5B).…”

“…Channel catfish ( I. punctatus ) were obtained from Guangdong Catfish Breeding Farm in Guangzhou (Guangdong, China), weighing 600 ± 150 g. They were maintained in a semi-automatic circulating water system (28) at 28 ± 2°C. Fish were fed for 3 weeks prior to any experiment, and all animal protocols were reviewed and approved by the University Animal Care and Use Committee of the South China Normal University.…”

“…The immunogen (TNP-KLH) was prepared as described previously (28, 32). TNP 1 -BSA and TNP 8 -BSA (19, 27) were employed as the antigen for antibody titer determinations and affinity and ELISPOT analysis.…”

“…As in mammals, these LLPCs provided a similar constant expression of specific antibodies over a 35-week period post-immunization in trout (19) and appeared to be primarily or entirely responsible for the long-term antibody responses in teleost (24). Although the form of the response may not be the same as in mammals (incorporating isotype switching, logarithmic increase in titer, and affinity), affinity maturation was still observed to occur in teleost over a TD antigen response (25–28). When affinity maturation occurred, the high-affinity antibodies appeared later, while the early appearance of low-affinity antibodies decreased over the response (16, 17, 19).…”

“…Until now, studies in channel catfish exposed to the protozoan parasite, Ichthyophthirius multifiliis , have suggested that long-term protective immunity seems to be provided by IgM + memory B cells rather than long-lived, non-dividing plasma cells (18, 30, 31). Our previous reports have demonstrated that, as in rainbow trout, affinity maturation occurs in catfish and high-affinity antibody subpopulations appear post-immunization with a T cell-dependent (TD) antigen, trinitrophenylated-keyhole limpet hemocyanin (TNP-KLH) (28). Thus, we proposed that LLPCs may exist in channel catfish, similar to rainbow trout.…”