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Abstract
Inflammatory acne has been elucidated by many researchers as a sort
of hypersensitivity reaction to bacterial components of Propionibacterium acnes (P. acne), but which one of the
immunological armies dominates in the pathogenesis of this type of
acne remains unclear. For this purpose we chose 20 acne patients (10
males and 10 females) matched with 5 normal controls. Assessment of
Fc receptors percentage on monocytes before and after vaccination by
P .acne had been done which revealed that Fc receptor percentage on
monocytes were significantly lower in patients with acne than in
control and increased after vaccine injection but still were
significantly lowered. So we concluded that cellular immunity plays
a major role in the pathogenesis of inflammatory acne than humoral
immunity.
Introduction
Acne vulgaris is a common, self-limited skin disease which involves the face
and upper trunk, manifested clinically by comedones, papules, pustules and
nodules. It usually affects individuals aged 20-40 years old.
The pathogenesis of inflammatory acne is not fully understood. While there is
increasing information about it, many questions remain to be answered. For
example, what causes the variety of distribution of the lesions in patients?
What factors are involved in the initiation of inflammatory lesion? What causes
follicular rupture, and what mechanisms are involved in the natural regression
of the disease in the majority of patients in mid twenties.[3]
Propionibacterium acnes contribute to the inflammatory nature of acne by
inducing monocytes to secrete proinflammatory cytokines including TNF-alpha,
IL-beta, and IL-8. In particular, IL-8 along with chemotactic factors may play
an important role in attracting neutrophils to the pilosebaceous unit.[5]
The mechanism by which P. acnes activate monocyte cytokine release is unknown
but is thought to involve pattern recognition receptors (PRRs) of the innate
immune system. Recently identified Toll-like receptors (TLRs) are one example of
PRR. Toll receptors can discriminate between Gram+ve and Gram-ve organisms,
bacterial ligands from Gram+ve bacteria can activate monocytes by TLR2 or
TLR4.[10,12]Activation of monocytes by P. acnes or its products may play a role
in the establishment of chronically inflamed acne lesions.[14]
Fc receptors are cell-surface receptors on monocytes for Fc domain of IgG and
defined by their ability to bind IgG-antigen complexes. This binding couples the
humoral and cellular immune responses and in the human, these receptors have
been divided into three classes based on differences in apparent molecular mass,
affinity for IgG, cellular distribution and reactivity with mAbs.[1, 2]
Fc receptors represent one of the important links between the antibody defense
mechanism and the cellular immunity in the form of phagocytosis.[7]
The aim of this work is to measure Fc gamma receptors of monocytes in
patients with varying degrees of acne vulgaris and normal controls in order to
assess the nature of humoral immune response to P. acnes. This of course will
help to concentrate more light on how mediation of inflammation in acne vulgaris
occurs.
Patients and methods
The study was carried out on ten age-matched healthy white
male rabbits, weighing approximately 2 Kg each. Animals were housed under the
same controlled environmental conditions at the animal house of the pharmacology
department, Alexandria faculty of medicine, fed normal laboratory diet and they
had free access to tap water.
Animals were anesthetized with thiopental sodium (2.5mg/kg
I.V.). Full thickness four circular excisional wounds were performed down to
bare cartilage on the ventral surface of each ear by using a 4-mm punch biopsy.
A magnifying binocular loupe C 2.3x340mm (Heine, USA) was used. Hemostasis was
then obtained by applying pressure. All wounds were covered using an occlusive
polyurethane dressing (Tegaderm 3M, Minneapolis, Minn.) until the entire wound
appeared re-epithelialized on gross examination.
Photographs were obtained and treatment of one of four
wounds per ear was begun immediately with quercetin cream three times daily for
four weeks. The second wound was treated with placebo cream at the same time to
serve as control for the preventive group (n=10). The remaining two wounds per
ear remained untreated during this period till a hypertrophic scar was
established. After four weeks, treatment of the third wound that developed
elevated scar was begun three times per day for eight more weeks. The fourth
wound was treated with placebo cream to serve as control group for the curative
group (n=10).
The ingredients in the cream were modified from the formula
according to Katsarou et al.[9] Each 100 gm cream contain:
quercetin (Carl Roth, GmbH co. 76185 Karlsruhe, Germany) 7.5 gm, white soft
paraffin 9.5 gm, liquid paraffin 4.75 gm, acetyl alcohol 3.5 gm, glyceryl
monostearate 2.5 gm, cremophor RH40 4.00gm, methyl paraben 0.25gm, propyl
paraben 0.10gm, propylene glycol 10.00gm and water to 100gm. The placebo control
was identical in composition except for quercetin.
With the animals under anesthesia, serial photographs were taken. The scars on
the left ear were carefully excised and stored at -80°C for use in the
biochemical measurements of: 1-Hydroxyproline concentration which is considered
a reflection of collagen content as it comprises approximately ten percent of
collagen.[10] 2-Histamine concentration was carried out according to the method
of Shore et al.[11]
Statistical analysis[12]: All data were expressed as mean
+ standard deviation (SD). One-way analysis of variance (ANOVA) techniques were
used to examine the studied parameters. For pairwise comparisons among groups,
the least significance difference test (LSD) was used. P value was calculated
and statistical significance was set at (P<0.05)
Results
The mean values of Fc receptor percentages in acne patients (males 35.2 and
females 37.6) were highly significantly decreased (P< 0.001), compared with
normal controls (males 89 and females 87,5) before P. acnes vaccination., as
illustrated in Figures ( 3, 4).
After P. acnes vaccine injections, the mean values of Fc receptor percentages on
monocytes appeared highly significantly increased (P<0.001) in both male
patients (62.4) and female patients (60.4), as shown in Figures (1,2). However,
they still appeared highly significantly lower (P<0.001) than those of normal
controls, as in Figures (5,6). On the other hand, there was no significant
difference (P>0.60) in the mean values of Fc receptor percentages in male acne
patients versus female patients, either before the vaccination or after, as
shown in Figures(7,8).
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Figure 1: Table & graph
show
the results of Fc receptor percentages in male acne patients before and
after vaccination |
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Figure 2: Table & graph
show
the results of Fc receptor percentages in female acne patients before and
after vaccination |
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Figure 3:Table & graph
show
the results of Fc receptor percentages in male acne patients before
vaccination compared to male controls |
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Figure 4: Table & graph show the results of Fc receptor
percentages in female acne patients before vaccination compared to female
controls
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Figure 5: Table & graph show the results of
Fc receptor percentages in male acne patients after vaccination compared to
male controls. |
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Figure 6 :
Table & graph
show the results of Fc receptor percentages in female acne patients
after vaccination compared to female controls .
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Figure 7: Table & graph show the results of Fc receptor percentages in male
acne patients versus female acne patients before vaccination .
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Figure 8: Table & graph show the results of Fc receptor
percentages in male acne patients versus female acne patients after
vaccination .
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Discussion
Acne vulgaris is considered as one of the most common
skin disorders, it can present in a variety of clinical forms depending on the
type, number and severity of predominant lesion. Thus, there may be mild,
moderate or severe comedonal or inflammatory acne, the latter with many
subtypes.
Webester (1998), concluded that the variability of
acne severity is due to the patient's reactivity to P. acnes. In other words,
inflammatory acne is due to hypersensitivity to P. acnes. The oversensitive
individual would mount a vigorous response to the organism, while the
non-reactive one would form no lesion at all. There is evidence that such
reactivity might be present in acne. In vitro complement activation by comedonal
material is stimulated by the presence of antibodies to P. acnes and greatly
decreased by their removal.[13]
Antibody to P. acnes is also required for neutrophil
lysosomal hydrolase release to be triggered.[9] Thus, in the presence of
elevated antibody titers, P. acnes is a much more potent and damaging
inflammatory stimulus. Patients with severe acne have elevation in immunity.
Antibody to P. acnes rises in proportion to the severity of acne
inflammation.[15]
Recently it has been found (Kim et al.,2002) that P.
acnes contributes to inflammatory nature of acne by inducing monocyte to secrete
proinflammatory cytokines including TNF-alpha, IL-lB and IL8. In particular, IL8
along with other P. acnes induced chemotactic factors that may play an important
role in attracting neutrophils to the pilosebaceous unit. The Fc receptors are
present on the phagocytic cells but are variable in molecular weight in each
group of cells, e.g., the molecular weight of the Fc receptors on monocyte is
80,000 while that on neutrophil is 43,000. At the same time, there are different
concentration of Fc receptors on different phage cells.[6]
In the human, leukocyte Fc gamma R are divided into
three classes (FcR1, Fc R2, and FcR3), each with their own function and
expression pattern. FcR1 binds monomeric IgG with high affinity whereas FcR2&R3
are of low affinity and only capable of binding IgG containing immune
complexes.[4]
In the present study, we used a mixture of the three
classes, hoping to extend our knowledge to FcR expression on human in vivo
situation. However, our results agree against the involvement of an immune
disorder in the etiology of inflammatory acne. Before P. acnes vaccine
injections, Fc receptor percentage values on monocytes were lower in acne
patients (males and females) than controls, and such a decrease was highly
significant (Figures 3,4). This may indicate that there were no enough Fc
receptors on monocytes to engulf the P. acnes organism, and subsequently, there
was no enough processing of the organism which can stimulate lymphocytes. The
decrease in Fc receptors could be interpreted by the possible presence of anti
Fc receptor like substances that could block Fc binding.[8]
After P. acnes vaccine injection (4 injections with
2 weeks in between), the percentage of Fc receptors increased with high
significance (Fig.5,6) this might be the cause of the partial (34%) improvement
rate in the patient's acne. A possible explanation is that the injected P. acnes
vaccine interacted by some way with the possible anti Fc receptor like
substances. Another explanation may be that P. acnes stimulated monocytes to
synthesize more Fc receptors. However, although this significant increase, still
Fc receptor percentages were highly significantly lower than those of control
group (Fig. 5,6) and this means that there is no role of humoral immunity in
acne vulgaris. However, the present study was devised to elucidate the mechanism
by which P. acnes induces inflammatory cytokines in monocytes by studying Fc
receptors on monocytes. It seems that recognition of microbial pathogens by the
cells of the immune system triggers host defence mechanisms to contact infection
to prevent disease. However, activation of these same pathways can also result
in inflammation at the site of disease and subsequent tissue injury. In acne the
host response to P. acnes can result in the production of inflammatory cytokines
and contribute to the clinical manifestations of the disease which is disruption
of the follicular epithelium and colonization of the follicles with P. acnes
with subsequent reactions in the surrounding dermis. The presence of other
receptors like TLRs on monocytes and their role in production of cytokines needs
a further research which we hope to be done in the future.
Summary & conclusion
Acne vulgaris is a disease of the sebaceous follicles and
is characterized by polymorphic skin lesions. These include open and closed
comedones, papules, pustules, nodules and cysts. Four factors are considered to
be important in the pathogenesis of acne; increased sebum production,
comedogenesis, the activity of the follicular microflora and inflammation.
This study attempted to spot light on some of the immunological factors that
may play a role in the pathogenesis of acne vulgaris. For this purpose, 20
patients (10 males and 10 females) aged 15-25 years complaining from acne
vulgaris and 5 normal controls (3 males and 2 females) were included in this
study. Blood samples were taken and submitted to estimation of Fc receptor
percentages on monocytes. A P. acnes vaccine was injected intradermally 4 times,
with 2 weeks interval with dose of 0.75 ml. The results were tabulated and
statistically analyzed.
It was found that, before P. acnes vaccine injections the mean values of Fc
receptor percentages in acne patients were highly significantly lower (males
35.2 and females 37.6) than those of normal controls (males 89 and females
87.5). After vaccination, the mean values of Fc receptor percentages were highly
increased in male and female acne patients (males 62,4 and females 59,6) but
still lower than control group. This mean that there is no role of humoral
immunity in acne vulgaris. Thus, we can conclude that cell-mediated immunity is
more detrimental than humoral immunity in the pathogenesis of acne vulgaris.
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