Novel site-specific mast cell subpopulations in the human lung.
BACKGROUND
Lung mast cells are stereotypically divided into connective tissue (MC(TC)) and mucosal (MC(T)) mast cells. This study tests the hypothesis that each of these subtypes can be divided further into site-specific populations created by the microenvironment within each anatomical lung compartment.


METHODS
Surgical resections and bronchial and transbronchial biopsies from non-smoking individuals were obtained to study mast cells under non-inflamed conditions. Morphometric and molecular characteristics of mast cell populations were investigated in multiple lung structures by immunohistochemistry and electron microscopy.


RESULTS
MC(T) and MC(TC) coexisted in all compartments, with MC(T) being the prevailing type in bronchi, bronchioles and the alveolar parenchyma and MC(TC) being more abundant in pulmonary vessels and the pleura. Each of the MC(TC) and MC(T) phenotypes could be further differentiated into site-specific populations. MC(TC) were significantly larger in pulmonary vessels than in small airway walls, while the reverse was observed for MC(T). Within each MC(TC) and MC(T) population there were also distinct site-specific expression patterns of the IgE receptor, interleukin-9 receptor, renin, histidine decarboxylase, vascular endothelial growth factor, fibroblast growth factor, 5-lipoxygenase and leukotriene C4 synthase (eg, bronchial MC(T) consistently expressed more histidine decarboxylase than alveolar MC(T)). Renin content was high in vascular MC(TC) but markedly lower in MC(TC) in other compartments. For both MC(TC) and MC(T), the IgE receptor was highly expressed in conducting airways but virtually absent in alveolar parenchyma.


CONCLUSIONS
These findings demonstrate novel site-specific subpopulations of lung MC(TC) and MC(T) at baseline conditions. This observation may have important implications in the future exploration of mast cells in a number of pulmonary diseases.
Andersson
C K
CK
Department of Respiratory Medicine and Allergology, Lund University Hospital, Lund, Sweden.
Mori
M
M
Bjermer
L
L
Löfdahl
C-G
CG
Erjefält
J S
JS
D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D016022:Case-Control Studies; D048430:Cell Shape; D048429:Cell Size; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D008168:Lung / Q000166:cytology* / Q000378:metabolism; D008297:Male; D008407:Mast Cells / Q000145:classification* / Q000378:metabolism / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D008875:Middle Aged; D020545:Respiratory Mucosa / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure
D036341:Intercellular Signaling Peptides and Proteins