2016, Volume 32, Number 1, Page(s) 022-026
Comparative Study of Mast Cell Count in Oral Reactive Lesions and Its Association with Inflammation
Hamideh KADEH, Ghazal DERAKHSHANFAR, Shirin SARAVANİ
Department of Oral & Maxillofacial Pathology, Oral and Dental Disease Research Center, School of Dentistry, Zahedan University of Medical Science, ZAHEDAN, IRAN
Keywords: Mast cells, Oral cavity, Inflammation
Reactive hyperplastic lesions are one of the most common lesions of the oral cavity. Mast cells can be found in various oral lesions. However, the exact role of mast cells in oral reactive lesions is not fully understood. The aim of this study was to compare the mast cells count in various oral reactive lesions and to evaluate the correlation between the mast cells number and the intensity of inflammation.
Material and Method: This cross-sectional study was performed on 80 samples of oral reactive lesions including irritation fibroma, pyogenic granuloma, peripheral giant cell granuloma and peripheral ossifying fibroma (20 for each). Eight samples of normal oral mucosa were selected as the control group. To determine the mast cells count and the intensity of inflammation, Toluidine blue and Hematoxylin & Eosin staining was performed respectively. The data was analyzed with SPSS (V.21), Kruskal-Wallis, Tukey and Spearman's correlation coefficient tests.
Results: In this study, a significant increase in mast cells count was found in oral reactive lesions compared to normal oral mucosa (p<0.001). Difference of mast cell count between irritation fibroma and the peripheral giant cell granuloma groups (p=0.023), peripheral ossifying fibroma and peripheral giant cell granuloma groups (p=0.001) was statistically significant. There was a significant correlation between mast cell count and the intensity of inflammation in the irritation fibroma and pyogenic granuloma groups.
Conclusion: The finding of this study showed that mast cells count in peripheral ossifying fibroma and irritation fibroma were significantly higher than normal oral mucosa, so mast cells may have some role in the induction of fibrosis in oral reactive lesions.
The oral mucosa is exposed to internal and external
stimulation constantly and therefore develops a range of
developmental, reactive, inflammatory and neoplastic
diseases. Reactive hyperplastic lesions are common in the
oral mucosa. These lesions are created in response to variety
of stimuli and damage caused by chewing, food impactions,
calculus, broken teeth and iatrogenic factors1
Kfir et al. classified reactive hyperplastic lesions as pyogenic
granuloma (PG), peripheral giant cell granuloma (PGCG),
peripheral ossifying fibroma (POF) and irritation fibroma
(IF)2. Despite chronic etiologic factors for all these lesions,
they have different histopathological characteristics3.
Mast cells (MCs) were discovered by Paul Ehrlich in 1878.
These are immune cells that originate from the bone
marrow and are scattered in all connective and mucosal
tissues especially perivascular area. Also they are seen in
the peripheral and central nervous systems. These include
numerous granules in their cytoplasm4-6.
MCs play a critical role in type 1 hypersensitivity
reactions. They also synthesize and release many different
chemical agents in response to various stimulations such
as histamine, prostaglandin, tryptase, chymase, various
cytokines (IL-3, IL-4, IL-5, IL-8, IL-13), as well as vascular
endothelial growth factor (VEGF), basic fibroblast growth
factors (BFGF) and transforming growth factor- ß (TGF-ß)7. Fibrosis is a collagen deposition process in which
fibroblasts are the target cells. MCs can affect fibroblasts
by releasing a wide range of biological active substances
and have a synergistic or antagonistic effect on them8.
MCs play a role in the pathologic fibrosis processes in
some conditions such as hypertrophic scars, chronic atopic
dermatitis, liver cirrhosis, fibrosing alveolitis and cardiac
The exact role of mast cells in connective tissue is not yet
fully understood. It is suggested that these cells have a role
in cell regulation and in the control of the accumulation of
connective tissue components10.
MCs have a critical role in the development of inflammation
in the oral mucosa in both early vasoinductive and acute to
chronic inflammation transition which suggests that mast
cells have a role in the employment of inflammatory cells
Since the role of mast cells in oral reactive lesions is still not
fully understood and only few studies have been done in
this subject4,6, the aim of this study to compare the mast
cell count in oral reactive lesions and normal oral mucosa
and also to determine the correlation between the number
of these cells and the intensity of inflammation.
In this cross-sectional study, all cases diagnosed as IF,
POF, PGCG and PG were obtained from the Department
of Oral and Maxillofacial Pathology in the Dental School
of Zahedan, Iran, over a period of 10 years. A total of 80
specimens were collected, including 20 cases for each
category. Also 8 clinically normal gingival tissues from
patients who had surgical removal for impacted third
molar were selected as control. Clinicopathological data
including age, gender and location were extracted from
the patients’ files. Specimens without clinicopathological
data and sufficient paraffin-embedded tumor tissues were
excluded. This study was approved by the ethics committee
of Zahedan University of Medical Sciences (Project No.
The paraffin-embedded tissues were segmented into 5 μm
sections. Two sections were prepared for each case; one
section was stained with 1% toluidine blue for detection of
mast cells and second section was stained with hematoxylin
and eosin for determination of the inflammation intensity.
In toluidine blue staining, mast cell granules are seen
purplish red and the nuclei sky blue in color.
All slides were observed by a pathologist that who was
blinded to the clinicopathological data for each specimen
using a light microscope (Nikon, Type2, Tokyo, Japan).
Evaluation of mast cell count was performed in 10
microscopic fields in the hot spot (the most populated
areas by mast cells) with a magnification of x400. Then the
total count of mast cells in 10 HPF was considered as the
mast cells count for each case. The inflammation intensity
was also evaluated according to the following scale (3):
0: absent; 1: mild (slight, scattered); 2: moderate (slightly
diffuse or prominent scattered inflammatory cells); and 3:
severe (prominent, diffuse).
Data analysis was performed using SPSS 21(SPSS Inc,
Chicago, IL), Kruskal-Wallis, Tukey and Spearman’s
correlation coefficient tests. A p-value less than 0.05 was
considered statistically significant.
This study was conducted on 88 samples, including 20 cases
of IF, 20 cases of POF, 20 cases of PG, 20 cases of PGCG
and 8 cases of normal oral mucosa. All demographic data
related to these samples are summarized in Tables I
In microscopic sections stained by 1% Toluidine blue,
mast cells are mostly found in the lamina propria and
perivascular area. They were predominantly located in
peripheral regions of the lesions in PGCGs (Figure 1A-D).
Click Here to Zoom
|Figure 1: Mast cells (arrows) in oral reactive lesions: A) Mast cells with granules in peripheral region of a peripheral giant cell granuloma
(Toluidine blue; x400). B) Mast cells in the superficial lamina propria and perivascular area in pyogenic granuloma (Toluidine blue;
x400). C) Mast cells in irritation fibroma (Toluidine blue; x400). D) Mast cells in peripheral ossifying fibroma with a focus of ossification
(Toluidine blue; x400).
Table III shows the average number of mast cells and
intensity of inflammation in various reactive lesions. The
average mast cell count in POF was higher than in all other
lesions (121.3 ± 50.04) and normal oral mucosa had the
minimum mast cell count (27.8 ± 20.4).
Click Here to Zoom
|Table III: Mean and standard deviation of mast cells count and
intensity of inflammation in study groups
According to the Kruskal-Wallis test, the difference of mast
cell count between study groups was significant (p<0.001).
In a comparison of the MC count between four study
groups, the Tukey test showed that only the difference
of mast cell count between IF and PGCG (p= 0.023) and
also between POF and PGCG (p= 0.001) was statistically
significant. In comparison of the number of the MCs
between each group and normal oral mucosa, the difference
of mast cell count between IF and normal oral mucosa (p
=0.018), and POF and normal oral mucosa (p=0.002) was
Using Spearman’s correlation coefficient test, there was
a significant correlation between mast cell count and the
intensity of inflammation in IF (r =0.445, p =0.049) and in
PG (r =0.732, p<0.001).
Mast cells have local and systemic effects by releasing a
variety of mediators in a degranulation process. Most of the
mediators are stored in cytoplasmic granules while other
mediators are released at the time of mast cell stimulation.
Importance and role of cytokines derived from mast cells is
not clear in some disorders. They may play a critical role in
both physiologic and pathologic processes10
The histopathology of oral reactive lesions is usually
dependent on the stage of the lesions which includes
neovascularization and inflammation11. Since mast cells
include cytokines that cause these processes, their existence
in these lesions may lead to better understanding of the
pathogenesis10. In the present study, the number of mast
cells in the oral reactive lesions was compared. Few studies
have been conducted for such a comparison.
According to our results, there was an increase in mast cell
count in reactive lesions compared to the normal mucosa
of the gingiva, which is similar to results from Farahani et
al.3, Reddy et al.10 and Shojae et al.6. In the present study, the mast cell count significantly increased only
in POF and IF when compared to the normal mucosa of
the gingiva that was similar to Reddy et al.10. However,
Shojae et al.6 reported a statistically significant difference
only between POF and normal oral mucosa. Farahani et
al. showed statistically significant differences between all
groups (IF, IFH, POF, PGCG) and normal oral mucosa3.
These differences are probably due to the type of technique
and sample size of the studies. In fact, POF and IF have a
more condensed fibrotic matrix compared to PGCG and
PG3, so the significant increase in mast cells count in
these lesions is probably a sign of chronic inflammation
that leads to fibrosis.
In vitro studies have shown the collagen synthesis and
metalloproteinase induction in pulmonary fibroblasts
caused by mast cells. In fact, mast cells can affect fibroblast
functional behavior, followed by fibrotic processes. This
process can be a result of the release of a series of fibrogenic
cytokines such as platelet derived growth factor (PDGF),
tumor necrosis factor (TNF-α) and basic fibroblast growth
factor (b-FGF). In addition, the main components in mast
cell granules are the tryptase and chymase enzymes that
have been proven to stimulate and induce the proliferation
of fibroblasts and type 1 collagen synthesis3,12.
In previous studies, it has been shown that the mast cell
count increases in lesions such as early stage of epulis13, submucosal fibrosis14, denture induced fibrous
hyperplasia (DIFH)7, inflammatory fibrous hyperplasia15 and solitary fibrous tumor16. In other studies, the
cross-reaction of mast cells with fibroblasts and their role
in collagen synthesis have been proven in diseases and
pathologic conditions such as scleroderma, fibrosis of skin17, and fibrotic transitions in minor salivary glands in
patients with Sjogren’s syndrome18.
Murata et al.13 showed that mast cells have a major role
in neovascularization of granulation tissue. However,
by increasing the fibrosis, the count of mast cells
decreases. They also mentioned that the other cells such
as macrophages and epithelial cells release fibrogenic
cytokines exactly like the mast cells13.
In our study, the mast cell count in PG was increased
compared to normal mucosa but this was not statistically
significant. In the Kamal et al.4 study, the average
count of intact and degranulated mast cells in PG was
significantly higher than the normal mucosa. In addition,
the average degranulated mast cell count was higher than
in intact cases. This proves that the number of mast cells
increases and degranulation occurs due to the stimulation by different etiologic factors. Then they cause vascular and
inflammatory changes that lead to PG formation. This
proves that mast cells may affect various stages of reactive
lesion formation and connective tissue4.
In this study, there was a positive correlation between
mast cell count and the intensity of inflammation in IF
and PG while in the Farahani et al. study3, there was the
same correlation in the IF and PGCG groups. This makes
it obvious that mast cells have a role in inflammation.
Chronic synthesis and release of TNF from mast cells may
cause leukocyte migration and chronic inflammation,
similar to what has been seen in lichen planus. Breakdown
of connective tissue matrix or structural proteins of
basement membrane that are produced by tryptase and
chymase of mast cells may facilitate the tissue diffusion of
leukocytes during the process of inflammation and other
inflammatory lesions such as lichen planus19. In our
POF and PGCG samples, there was no correlation between
mast cell count and intensity of inflammation which is
similar to the Smith et al. study20.
In conclusion, mast cells may have a role in the pathogenesis
of the oral reactive lesions and induction of fibrosis. They
may also be one of the factors that cause a variation in
microscopic features in this kind of lesions with a common
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