Development of T cell lineages and the role of the thymus as a source of immature T cells in parotid (PG) and submandibular salivary glands (SMG) were studied in Fischer 344 rats using the Thy-1/CD45RC/RT6 expression model. In addition, the phenotypes of salivary gland lymphocytes were compared with other conventional and extrathymic populations. PG mononuclear cells consisted of T cells (38%), B cells (29%), and NK cells (4%). SMG had 19% T cells, 7% B cells, 37% NK cells, and an unusual population of CD3−/RT6+ cells. In comparison with lymph node (LN), both PG and SMG were enriched in immature (Thy-1+) and activated (Thy-1−/CD45RC−/RT6−) T cells. Unchanged percentages of Thy-1+ T cells in PG and SMG following short-term adult thymectomy indicated that immature salivary gland T cells had an extrathymic source. In contrast, thymectomy eliminated LN recent thymic emigrants. SMG had T cells with characteristics of extrathymic populations, expressing TCRγδ+ (28%), the CD8αα homodimer (11%), and NKR-P1A (66%). Many SMG T cells expressed integrin αEβ7. PG T cells resembled those isolated from LN in respect to TCR and CD8 isoform usage, but were enriched in αEβ7+ T cells and in NKT cells. Thus, salivary gland mononuclear cells are composed of a variety of subpopulations whose distributions differ between SMG and PG and are distinct from LN. These studies provide a basis for further investigation of regionalization in the mucosal immune network and are relevant to the design of vaccine regimens and intervention during pathological immune processes.

No abstract

The subset distribution of lymphocyte populations isolated from rat lacrimal glands (LG) was compared with those from tissues of both mucosal and non-mucosal origin. In spleen (SPL), mesenteric (MLN) and cervical lymph node (CLN) populations the percentages of cells bearing W3/13 (pan T) and OX19 (pan T) were greater than the percentages obtained for cells bearing the OX7 (Thy-1) marker. In contrast, for lacrimal (LG), salivary (SG) and mammary gland (MG) populations, cells bearing OX7 predominated over those bearing the W3/13 and OX19 markers, with the exception of day 1 post-partum MG tissue which displayed equal numbers of OX7 and OX19 cells. Except for MG, in which OX8 (T non-helper) predominated over W3/25 (T helper) populations, the proportions of these two subsets in the other tissues were generally similar. Analysis of SPL and LG cells for coexpression of OX7 with OX19 or L chain indicated that significant percentages of OX7 bearing cells also expressed T or B cell markers. However, the higher values noted for the OX7 population in LG were not attributable to increased numbers of cells coexpressing pan T or B cell markers. These findings show that lymphocyte subset distribution in LG and other glandular mucosal tissues is distinct from that of non-mucosal tissues, in that mucosal tissues contain a predominance of cells bearing the Thy-1 (OX7) phenotype.

Marker expression was studied in rat lymphocyte populations isolated from parotid, submandibular and sublingual salivary glands. Comparative data were also obtained for lacrimal gland and spleen populations. Increased percentages of Thy-1+ cells were found in salivary gland populations when compared to spleen with the highest percentage noted for parotid gland. Thy-1 percentages in parotid gland were comparable to those obtained with lacrimal gland. Salivary gland sIg, CD5 and CD8 cell percentages were lower than those obtained for lacrimal gland and splenic populations. The percentages of CD4-bearing cells in submandibular and sublingual gland were lower than those found in parotid gland, lacrimal gland and spleen, and the CD4:CD8 ratios in parotid gland most closely approximated those in spleen. Increased percentages of Thy-1+ lymphocytes coexpressing sIg and CD5 were obtained for all salivary gland cell populations when compared to spleen; however, percentages of salivary gland cells bearing these 3 markers were lower than noted for lacrimal gland, which contained the highest percentage. With respect to adhesion molecules, lymph node homing receptor (LNHR) and Peyer's patch homing receptor (PPHR) bearing cells were found in all glandular populations with the percentages of LNHR+ exceeding PPHR+ lymphocytes. Homing receptor bearing populations were highest in spleen and were present in equal proportions. LFA-1 was expressed by all salivary gland cell populations in greater percentages than lacrimal gland, but lower than those in spleen. VLA-4 and CD44 expression was higher in parotid gland and spleen than in submandibular and lacrimal gland. These data show that the phenotypes of resident lymphocytes in salivary gland tissues differ from lacrimal gland and spleen, as well as each other, and indicate that Thy-1+ cells in glandular tissues bear both B and T cell markers. The adhesion molecule expression data suggest that these molecules may be utilized differently in various glandular tissues, potentially contributing to the variation in phenotypic profiles of resident glandular lymphocytes.

No abstract