ULTRASTRUCTURAL IDENTIFICATION OF THE SPLENIC FOLLICULAR DENDRITIC CELLS IN THE CHICKEN

Background: There is a need to identify the follicular dendritic cells (FDC) of the chicken spleen at the ultrastructural level during a sec ondary immune response. Methods: The cells were identified after intra venous priming BSA and boosting with biotinylated BSA conjugated to co lloidal gold particles. Monoclonal antibodies raised specifically eith er 60 chicken IgG or IgM were used to characterize these immune comple x-trapping cells. Results: The FDC had an irregular morphology which v aried through time, supporting the existence of two types of FDC in th e chicken spleen, one showing filiform cell processes, the other provi ded with beaded dendrites. When the filiform dendrites were observed, the FDC bound the antigen on their surfaces. These dendrites showed an intrincate convoluted configuration, forming tightly wrapped networks near the cell body. The networks had the same features as those descr ibed in mammals as antigen retaining reticulum (ARR). In chickens, the ARR, which represents sites of antigen localization on FDC, reached m aximum development on day 5 after the second injection of BSA and had disappeared by day 8. At this time FDC had beaded dendrites. Conclusio ns: Antigen is retained on FDC in the chicken spleen for long periods of time. (C) 1995 Wiley-Liss, Inc.