Lymphocyte populations and adhesion molecule expression in bovine tonsils

Bovine tonsils are mucosal-associated lymphoid tissue (MALT) located at the entry of the pharynx when both inhaled and ingested antigens can induce an immune response. This study was conducted to determine the lymphocyte popu lations and adhesion molecule expression in the palatine tonsil (PT) and ph aryngeal tonsil (PhT) of adult cattle and compare them with typical MALT (d iscrete Peyer's patches, PP) and a peripheral lymph node (parotid lymph nod e, PLN). The distribution of various lymphocyte subsets was determined in s itu by immunofluorescence, and their proportions were determined by multico lor flow cytometry. The tonsils were similar to PP in the proportions of B- and T-cells (25-32% T-cells, 39-45% B-cells), and T cell subpopulations (C D4, CD8, and gamma delta). The PP contained the highest proportion of memor y T-helper cells with beta 7 integrin (30.3% +/- 5.4), the tonsils intermed iate (PT: 19.8% +/- 4.4 and PhT: 19.7% +/- 4.9), and the PLN had the lowest proportion (15.4% +/- 3.1). The opposite relationship was observed with CD 62-L on naive T-helper cells as PP had the lowest proportion (14.2% +/- 6.4 ), the tonsils intermediate (PT: 17.4% +/- 2.5 and PhT: 24.3% +/- 7.3), and the PLN the highest proportion (45.3% +/- 6.5). MAdCAM-1 was highly expres sed in the high endothelial venules (HEV) of PP, with variable and weak exp ression in the tonsils and PLN. PNAd, on the other hand, was highly express ed in HEV of tonsils and PLN, and weakly expressed in the PP. These results indicate that the bovine tonsils share characteristics with both PP and PL N. The alpha 4 beta 7/MadCAM-1 and CD62L/PNAd interaction may be involved i n lymphocyte migration to the tonsils, but it is likely that other adhesion molecules participate as well. Similarities between the human and bovine t onsils suggest that cattle may provide a good model to study the role of th e tonsil in the respiratory immune response. (C) 2000 Elsevier Science B.V. All rights reserved.