Actin-Like Protein in Chicken and Mammalian Lymphoid Tissue Demonstrated by Reactivity with Human Smooth Muscle Autoantibody

Abstract

The reactivity of chicken, human, rat and mouse lymphoid tissues with human serum containing smooth muscle antibody was studied by indirect immunofluorescence. In bursal follicles, strong fluorescence was observed predominantly in the lymphocytes and reticular epithelial cells of the medulla, the basement membrane and a row of undifferentiated epithelial cells at the corticomedullary junction. Reticular epithelial cells in lymphocyte-depleted bursas from cyclophosphamide-treated chickens and cultures of bursal and thymic reticular epithelial cells also reacted with smooth muscle antibody. The thymus of all species showed only medullary staining; lymph nodes, spleen and gut-associated lymphoid tissue showed extensive cell staining of both T and B lymphocyte dependent areas, with weak reactivity in germinal centres. Embryologically, the time of appearance of bursal and thymic lymphocyte staining coincided with the development of medullary lymphocytes. In organ imprints and cell smears of bursa, thymus, lymph node and spleen, and in cell smears of bone marrow and peripheral blood lymphocytes, immunofluorescent staining was restricted to cells in close contact with each other. Suspensions of dispersed viable lymphoid cells were negative. Specificity of the staining reaction was established by its prevention after neutralization: absorption of the serum with homogenates of smooth muscle or actin derived from the same source. It is concluded that an actin-like protein is present in mature B and T lymphocytes and in reticular epithelial cells and that its expression in lymphocytes appears dependent on cell-to-cell contact. The presence of the actin-like protein in mature lymphocytes may provide a means of lymphocyte motility in vivo.

Contact-Dependent Expression of Actin in Chicken Lymphocytes in vitro

“…This supports previous immuno fluorescence studies on chicken cells [2] and mouse B cells [6] but is in contrast to earlier proposals [5] that actin was specific for T cells. The more effective re duction in AAA by absorption with spleen indicates these cells have a higher concentration of actin than those of the bursa or thymus.…”

“…As reported earlier [2], immunofluorescence with AAA on cell smears was restricted to cell borders at The time dependence and relative effectiveness of thymus, bursa and spleen lymphocytes for contact-in duced expression of actin are summarized in table I. Spleen cells exhibited a more rapid and more intense cell border staining of actin following mem brane-membrane contact, than those of the thymus, while bursa was the least effective. The time taken for cell settling was also important for maximum fluores cence, 30 min being optimal.…”

“…In our studies on anti-actin antibody (AAA) im munofluorescence staining of lymphocyte smears, we observed that expression of actin was restricted to cells in close contact with other cells, the fluorescence being localized to the junction areas [2], This suggest ed microfilament aggregation as a result of membrane stimulation. In this paper we report further studies on the nature of this membrane-contact dependent ex pression of actin.…”

“…To complement our earlier studies using immuno fluorescence [2], the presence of actin in chicken bursa, thymus and spleen lymphocytes was demon strated by sequential absorptions of AAA with pack ed cells which had been disrupted by freeze-thawing to release cytoplasmic actin. The results are presented in figure 1.…”

“…These reagents have thus been used extensively to demonstrate actin in a varie ty of non-muscle cells [7,14], including both T and B lymphocytes [2,[4][5][6]. Actin can exist as a soluble amor phous form or aggregated into microfilamentous [15] structures, expression of which depends on a number of factors including the state of differentiation of the cell [2,13] and membrane activation [5]. Together with microtubules they constitute a cytoskeletal system linking plasma membrane receptors with the cyto plasm [12,19].…”