Conjunctival-associated lymphoid tissue: evidence for a role in the secretory immune system.

A specialized lymphoid tissue in rabbit conjunctiva was studied by various histologic and immunologic techniques and compared with similar structures along other mucosal surfaces. The flattened conjunctival lymphoepithelium overlying the lymphoid follicles was devoid of goblet cells. This lack of goblet cells is characteristic of epithelium overlying similar lymphoid collections in gut and bronchus. The lymphoid follicles demonstrated neither intra- nor extracellular immunoglobulin, and the lymphocytes in these follicles were composed of B-cells and T-cells, when studied by various immunologic techniques. A high proportion of these lymphocytes showed surface immunoglobulin A (IgA), and a high proportion of IgA precursors were determined by pokeweed mitogen (PWM) stimulation in 4-day cultures. The morphologic and immunologic results are similar to those obtained from gut and bronchus, tissues known to disseminate lymphoid cells to other mucosal sites already committed to antigen and IgA isotype. It is speculated that conjunctival associated lymphoid tissue of rabbit is part of a generalized system of secretory immunity capable of sampling conjunctival applied antigen, and then disseminating cells committed to IgA antibody production to other mucosal sites.