Characterization of Two Major Populations of Lung Fibroblasts: Distinguishing Morphology and Discordant Display of Thy 1 and Class II MHC

Abstract

We have determined that murine lung fibroblasts are divisible into two major subpopulations based on expression of Thy 1. Twenty-four to fifty-three percent of freshly isolated lung cells displayed Thy 1 and were separated using FACS into Thy 1+ and Thy 1- fractions for morphologic examination. Analysis by electron microscopy revealed that both the Thy 1+ and Thy 1- fractions contained fibroblasts. Freshly isolated lung cells cultured for 2 wk consisted of greater than 95% fibroblasts, with 28 to 49% displaying Thy 1. These cells were sorted by FACS into Thy 1+ and Thy 1- lines that maintained a stable phenotype over many weeks and that were used as a source to obtain stable fibroblast clones. Adherent pulmonary fibroblasts are not phagocytic and lack the markers of macrophages, dendritic cells, B lymphocytes, and T lymphocytes (with the exception of Thy 1). Interestingly, the Thy 1- fibroblasts spread more and contained a more extensive microfilament and microtubule network than did the spindly and often lipid-containing Thy 1+ population. Both populations of fibroblasts synthesized collagen. Class I MHC expression was very low on Thy 1+ and Thy 1- fibroblasts, but high levels were displayed after gamma-IFN treatment. Most exciting was the unexpected finding that only the Thy 1- lines and clones displayed class II MHC (Ia) in response to treatment with gamma-IFN. Moreover, only the Thy 1- fraction (gamma-IFN-treated) presented antigen to T lymphocyte clones, an observation that suggests that this subset of cells may be involved primarily in promoting chronic lung inflammation, which is associated with developing fibrosis. Thus, two populations of pulmonary fibroblasts exist, defined by the expression of Thy 1, distinguishing morphology, inducibility for Ia expression, and antigen-presenting function. It should now be possible, using these characteristics, to ascertain the role of pulmonary fibroblast subpopulations in developing fibrosis.

Thy-1 Expression in Human Fibroblast Subsets Defines Myofibroblastic or Lipofibroblastic Phenotypes

“…9 Beside differential functional attributes, there also exists phenotypic diversity within fibroblast populations. Differences in morphology, 10 and cell size 11,12 have also been reported in fibroblast strains from various tissues. Phenotypic heterogeneity may further suggest different functional properties between fibroblast subpopulations.…”

“…32 Furthermore, using Thy-1 as the discriminatory cell surface marker, we successfully separated mouse lung and spleen and human myometrial and orbital primary fibroblast strains into bona fide Thy-1 ϩ and Thy-1 Ϫ subsets, and these were shown to display distinct functional properties. 7,10,30,33 In particular, human myometrial Thy-1 ϩ and Thy-1 Ϫ subsets exhibited differences in cytokine and prostaglandin production, CD40 expression, and cyclooxygenase localization. 30,34 Human orbital fibroblast subpopulations were heterogeneous with respect to cytokine and prostaglandin production and MHC class-II expression.…”

“…27,28 In the past decade, we established that the surface receptor Thy-1 is heterogeneously expressed in fibroblast strains from many tissues. These included mouse lung and spleen, 7,10 human lung, myometrium, and orbit. 29 -31 Thy-1 is a cell-surface glycoprotein, whose function remains illdefined.…”

Deep dermal fibroblasts contribute to hypertrophic scarring

“…59 Phenotypic diversity also exists within fibroblast populations, along with differences in morphology 60 and cell size. 61,62 In this study, we have presented evidence that dermal fibroblasts from different depth of skin are highly heterogeneous and the deeper layer cells most closely resemble the HTS fibroblast phenotype.…”

Bone-Marrow Chimeras Reveal Hemopoietic and Nonhemopoietic Control of Resistance to Experimental Lyme Arthritis

“…Similarly, TNF-␣ can be locally produced by synovial tissue cells and is a pivotal cytokine in the pathogenesis of rheumatoid arthritis and collagen-induced arthritis (41,42). Furthermore, fibroblasts, even those from a single tissue, are composed of cellular subsets, much like lymphocytes (43,44), and those from different anatomic regions display distinct phenotypic characteristics (45). Thus, it is possible that these differences among fibroblasts may not only control genetic resistance and susceptibility to pathology, but may even be the basis for its tissue specificity.…”