The lymphoid follicles of the human palatine tonsil.

The distribution of immunoglobulin (Ig) in the lymphoid follicles of the human palatine tonsil has been re-examined by applying the unlabelled antibody peroxidase–anti-peroxidase (PAP) sequence and a two-stage fluorescein isothiocyanate (FITC) technique to trypsinized paraffin sections and cryostat sections. Large numbers of cells containing Ig were demonstrated in the follicle centres, γ, μ, δ and α heavy chains being present. Cells containing κ and λ chains were found in all follicle centres, a finding incompatible with the monoclonality of the centres. Extracellular Ig (γ, α, μ and δ heavy chains, κ and λ light chains) was also present in the follicle centres. The lymphocytes of the mantle (zone C) appeared to have μ and δ chains (and κ and λ chains) on their surfaces, and were considered to be immature B cells, thereby providing support for our earlier hypothesis that these cells constituted a pool of B memory cells. Trypsinized paraffin sections proved superior to cryostat sections for the demonstration of intracellular Ig, but the reverse was true for surface Ig. Extracellular Ig was equally evident in both types of section. The metalophil method of Marshall (1948) revealed dendritic histiocytes in the follicle centre and lymphocyte mantle (zones B and C). The follicles were supplied by one or more prominent arterioles, around which the dendritic cells were located, an arrangement which may function as a `traffic area' for trapping circulating B cells on the antigen-bearing dendritic cells.