Lymphocyte and macrophage subpopulations and the stroma of mucosa-associated lymphoid tissue in the nasal cavity of the rat were examined by application of immunohistochemical and enzyme histochemical methods to cryostat sections. Nasal-associated lymphoid tissue was composed of a loose reticular network with lymphocytes and macrophages, covered by epithelium. The epithelium was infiltrated with B cells. T helper (W3/13-positive) and T suppressor/cytotoxic or large granular cells (OX8-positive), ED1-positive macrophages and Ia-positive cells. The B cell areas were populated by B cells, immunopositive for surface IgM or IgG. B cells with surface IgA or IgE were rare. Germinal centres were found infrequently. T helper cells were scattered throughout the B cell area. A few ED1-positive macrophages and ED5-positive follicular dendritic cells were observed. Strong Ia staining (mostly of B cells) was found in this area. The T cell areas contained T helper and T suppressor/cytotoxic cells in about equal amounts, and numerous ED1-positive macrophages. ED1 staining was also found in the subepithelial area. Numerous ED1-, ED2- and ED3-positive macrophages were found in the border between the lymphoid mass and the surrounding connective tissue. A few non-lymphoid cells showed weak acid phosphatase or non-specific esterase activity. The morphological observations suggest that nasal-associated lymphoid tissue plays an important role in the first contact with inhaled antigens.

Summary In order to study the role of nasal-associated lymphoid tissue (NALT) in the local nasal immune response, rats were immunized intra-nasally with either ofthe following trinitrophenylated (TNP) antigens; the thymus-dcpendent keyhole limpet haemocyanin (KLH). or the thymusindependcnt lipopolysaccharide (LPS), or with the particulatc (thymus-dcpendent) sheep red blood cells (SRBC). Primary responses hardly occurred, while only TNP-KLH elicited a considerable secondary response. The major responding organ was the posterior cervical lymph node. Specific antibody-forming cells (AFC) occurred in the medulla and were mainly of the igA or IgG isotype. Hardly any specific AFC were found in NALT or the surrounding mucosa. Intranasal immunization evoked no antibody response in the lung. Ample anti-TNP antibodies could be detected in the sera of animals, primed and boosted with TNP-KLH or TNP-LPS. No specific serum antibodies occurred after immunization with TNP-SRBC. The results arc discussed in vicwof the immunoiogical defence in the upper respiratory tract.

Immunohistochemical staining of biopsy specimens was used to investigate the occurrence of lymphocyte subsets and non-lymphoid cells within the epithelial layer of the human nasal mucosa. The CD 19 (B cell) marker was not expressed on the intra-epithelial lymphocytes, whereas the pan T cell marker CD2 was varyingly detected. The HLA-Dr antigen was abundantly present on epithelial cells, lymphocytes, and non-lymphoid cells. The latter are probably dendritic or Langerhans’ cells. The findings stated above were the same in patient and control samples. In biopsy sections of 9 ear, nose, and throat patients, many CD8-positive (T suppressor/cytotoxic) cells and very few weakly stained CD4-expressing (T helper/inducer) cells were present. Quantification on single-cell preparations showed an average of 67% of the lymphocytes to be CD2 positive, 73% to be CD8 positive, while only 12% of the lymphocytes expressed the CD4 antigen. In control sections CD8 was similarly present as in patient sections, and, in addition, some clearly stained CD4-positive cells were seen.

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