ORGANIZATION AND CYTOLOGY OF LYMPHOID-TISSUE IN THE CYNOMOLGUS MONKEYCONJUNCTIVA

Background: Knowledge of the structure of conjunctival lymph follicles is limited in comparison with those of other mucosa, Consequently a t horough morphological study of the follicles was undertaken to see if they are similar to others or whether they have any unique features an d to provide an adequate background for future experimental studies. M ethods: Normal lymphoid tissue of the conjunctiva of one side of nine young adult cynomologus monkeys was examined using a whole mount metho d and light and electron microscopy. Results: Only the peripheral tars al and orbital regions of the upper and lower palpebral conjunctiva co ntained lymph follicles. Lymphocytes, reticulocytes, macrophages inclu ding tingible body macrophages, putative follicular dendritic cells, a nd plasmacytes were identified in the follicles and M-cells were prese nt in the follicle associated epithelium. High endothelial venules (HE V) displaying evidence consistent with lymphocyte extravasation were p resent in both primary and secondary follicles. A majority were second ary follicles with a germinal center composed largely of lymphoblasts, Mitoses were found in secondary follicles, mostly confined to the ger minal centers, and they were numerous in many. Increased cell density and virtual elimination of intercellular space adjacent to some high e ndothelial venules suggested a possible association of these vessels w ith germinal center development. Chains of follicles were linked by ly mph vessels, an approaching lymphatic dividing to embrace a follicle a nd recombining beyond it and passing to the next in line; many conjunc tival follicles therefore have both afferent and efferent lymphatics, The vessels were in direct contact with the follicle perimeters; lymph capillaries were not present within the substance of most follicles, Numerous valves indicated drainage radially from the tarsal conjunctiv a then laterally or medially from the orbital conjunctiva through the follicle chains towards the nearest canthus. Conclusions: Conjunctival lymph follicles are fundamentally similar in structure to those found elsewhere in the body. However, the beads on a chain-like arrangement of lymph vessels and follicles may be unique, The possible associatio n of HEV with follicle formation could be a general characteristic of mucosal follicles. (C) 1995 Wiley-Liss, Inc.