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The Follicular Dendritic Cell: Long Term Antigen Retention During Immunity

The obligatory need for antigen in the induction of a specific immune response has long been recognized. However, much less in known about the possible continuing requirement for antigen for the maintenance of adequate levels of immunity. If immunity is to be protective, the maintenance of an adequate level of immunity, cellular and/or humoral, is as important as is its induction. There is a vast body of evidence demonstrating that once a satisfactory degree of immunity has been produced, it tends to be maintained by the continued production of antibody as well as by a well developed capacity to respond rapidly and accurately to a fresh antigenic challenge. In humoral immunity it has long been known that antibody levels can be maintained for very long periods even in the absence of fresh exogenous immunogenic stimulation. The possible role of retained antigen in regular restimulation of specific memory cells has been postulated and it has been suggested that small quantities of antigen are retained as antigen-antibody complexes at certain strategic sites such as lymphoid organs (Graf & Uhr 1969, Bystryn et al. 1970, 1971, Kitces et al.