Nucleolar silver staining patterns and HLA-DR antigen expression in bronchial epithelial cells in chronic bronchitis

Expression of genes for B7-H3 and other T cell ligands by nasal epithelial cells during differentiation and activation

Epithelial cells of the human respiratory tract express human leukocyte antigen (HLA) and the costimulatory molecules B7-1 and B7-2. Little is known, however, about the constitutive expression of genes encoding for the more recently identified members of the B7 homolog family of costimulatory molecules or about the influence of cellular differentiation and cytokines on their activity or on that of HLA or B7-1 and B7-2. Human nasal epithelial (HNE) cells were grown at the air-liquid interface (ALI) for 2 or 21 days to model in vivo conditions. Expression of genes for HLA-B and HLA-DR1 increased during mucociliary differentiation during this period and became more similar to HNE cells obtained fresh by brush biopsy from nasal turbinates. Gene transcripts for B7-H3 and B7-H2 were abundantly expressed in cells cultured at the ALI, but neither their activities nor that of B7-2 was significantly altered during differentiation. IFN-gamma and TNF-alpha upregulated mRNA encoding for both HLA molecules, but not for the B7 molecules. This study describes, for the first time, the expression of B7-H3 and B7-H2 by HNE cells and thus expands the range of potential costimulatory signals through which these cells may interact with activated mucosal T lymphocytes. In addition, the results suggest that the extent of mucociliary differentiation of cultured cells may influence this capability.

Constitutive expression of MHC and adhesion molecules by alveolar epithelial cells (type II pneumocytes) isolated from human lung and comparison with immunocytochemical findings

Highly purified populations of alveolar epithelial cells (type II pneumocytes) were isolated from human lung specimens. These cells were characterised histochemically, by demonstrating the presence of intracellular alkaline phosphatase, and morphologically, by electron microscopic demonstration of lamellar bodies and microvilli. Expression of the epithelial glycoprotein HEA-125, of MHC class I and class II (HLA-DR, -DP and -DQ) antigens and of the intercellular adhesion molecules ICAM-1, VCAM-1, LFA-3 and B7 was quantified by flow cytometry. Comparison was made between the expression of these molecules by isolated type II cells and by alveolar epithelium in normal human lung tissue after immunocytochemical staining of frozen sections of donor lung. Isolated type II pneumocytes expressed HEA-125 and class I MHC molecules and the class II MHC molecules HLA-DR and -DP; HLA-DQ was not detected. The intercellular adhesion molecule ICAM-1 was expressed constitutively at low levels but there was minimal expression of VCAM-1, LFA-3 and B7. It was not possible to differentiate type II cells from the predominant type I pneumocytes on frozen sections. Alveolar epithelium expressed HEA-125, class I MHC antigens, the class II molecules HLA-DR, and -DP and the intercellular adhesion molecule LFA-3. Expression of the adhesion molecules ICAM-1, VCAM-1 and B7 was variable. As with the isolates, HLA-DQ was not observed on alveolar epithelium. In conclusion, a reproducible method for the isolation of pure populations of human type II pneumocytes has been developed. These cells were not damaged by the isolation procedure. It is not known whether alveolar epithelium can present antigens to T lymphocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

The nucleolus

Nucleoli are the sites of biosynthesis of the ribosomal precursors. They contain may copies of the genes for the main rRNAs (18S- and 28 S-rRNA) in the form of tandemly arranged repeats at the chromosomal nucleolar organizer regions (NORs). They also contain the small rRNA (5S-rRNA) that is synthesized outside the nucleolus, specific nucleolar proteins, among them the factors and enzymes necessary for transcription and transcript processing, and the precursor units of the ribosomes. In man as in may vertebrate species, three main components of nucleoli, besides chromatin, can be detected: fibrillar centres (FC), dense fibrillar component (DCF), and granular component (GC). Within a nucleolus the FCs are in many cases situated in its central region. The DFc forms a network of strands surrounding the FCs, but may sometimes reach for out towards the periphery of the nucleolus. The GC is usually situated in the peripheral regions of the nucleolus. In cells with a low level of ribosomal biosynthesis the nucleoli are small, usually with a single FC and little surrounding DFC and GC ("ring-shaped nucleolus"). In active cells the DFC forms a large network enclosing several, sometimes up to hundreds of FCs, and the GC covers a large area in the periphery ("compact nucleoli"). In cells at the onset of a new stimulation, the DFC is very prominent whereas the FCs are few and small, and the GC is also not very extensive ("reticulate nucleoli"). In some special cell types that are very active other arrangements of the structural components are found. In Sertoli cells, for instance, only one nucleolus is found, or occasionally two, each with a single large FC and a distinct area of GC, both areas being engulfed by DFC intermingled with some peripheral GC. Immunocytological and in situ hybridization studies to localize the rRNA genes within the nucleolus have so far led to divergent results. Both fibrillar components, the FCs and the DFC, have been claimed as the most probable candidates. Transcription of rDNA and the subsequent early steps of ribosome biosynthesis are localized in the DFC, whereas later steps (mature rRNA, preribosomes) are localized in the GC. The FCs may also serve as sites for the preparation of the rDNA for transcription, and as a store for certain nucleolar proteins. During mitosis, parts of the nucleolar proteins remain at the NORs. A direct contact between the nucleolus and the nuclear envelope is frequently observed but is not dependent on nucleolar activity.(ABSTRACT TRUNCATED AT 400 WORDS)