Year : 2008 | Volume
: 51 | Issue : 2 | Page : 172--174
Evidence for eosinophil degranulation in acute appendicitis
G Santosh, KP Aravindan
Department of Pathology, Medical College, Calicut - 673 008, Kerala, India
K P Aravindan
Medical College, Calicut - 673 008, Kerala
Finding of increased numbers of eosinophils in the muscle in cases of acute appendicitis has led to the hypothesis that it may have an allergic origin. This study aimed to measure the eosinophil degranulation resulting in a rise in the serum of eosinophil granule proteins that would be expected in such cases. The levels of serum eosinophil cationic protein (ECP) measured by chemiluminescence assay in acute appendicitis were compared, with those of appropriate controls. Mean (95% CI) serum ECP (µg/L) levels were: acute appendicitis 45.3 (27.7-63.0); normal appendix 22.7 (16.0-29.3); asthma 24.2 (4.6-43.8); and healthy volunteers 13.2 (8.3-18.1). In cases of acute appendicitis, there is an inverse relationship between duration of symptoms and serum ECP. However, this was not statistically significant. Significant local eosinophil activation and degranulation occurs in acute appendicitis, enough to cause a rise in serum levels of eosinophil chemotactic protein
|How to cite this article:|
Santosh G, Aravindan K P. Evidence for eosinophil degranulation in acute appendicitis.Indian J Pathol Microbiol 2008;51:172-174
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Santosh G, Aravindan K P. Evidence for eosinophil degranulation in acute appendicitis. Indian J Pathol Microbiol [serial online] 2008 [cited 2019 Dec 11 ];51:172-174
Available from: http://www.ijpmonline.org/text.asp?2008/51/2/172/41642
The prominent theories regarding etiopathogenesis of acute appendicitis are as varied as mechanical obstruction to allergy and free radical injury to ischemia.
Allergic etiology for acute appendicitis was proposed for the first time by Aravindan.  The finding of eosinophil infiltration of muscle layer with splitting of muscle fibers due to intramuscular edema in cases of acute appendicitis suggested the possibility of a type 1 hypersensitivity reaction behind initiation of the disease. If eosinophils are not just innocent bystanders, there would be serological evidence of eosinophil degranulation which can be detected. Serum level of eosinophil cationic protein (ECP) has shown good correlation with eosinophil activation and degranulation and has been studied extensively in conditions like bronchial asthma and atopic dermatitis.
In this study, we have tried to verify the postulated allergic etiology of acute appendicitis by measuring serum ECP as a marker for eosinophil degranulation.
Materials And Methods
The study subjects and controls were as follows:
Cases: Histologically proven acute appendicitis (18 patients).
Patients whose appendicectomy specimens are histologically normal (six patients)Sera from five healthy volunteersSera from three cases of acute bronchial asthma
The appendicectomy cases were consecutive ones collected in a period of 1 month and in which the exclusion criteria did not apply.
Skin disease, asthma, or other allergic disorders.
Clinical examination: Patients where personally interviewed at time of admission and all relevant clinical and laboratory data collected.
Blood collection: Blood was collected at admission from patients clinically diagnosed to have acute appendicitis and who were likely to undergo emergency appendicectomy.
Two milliliters of blood was collected from cases and controls by venupuncture in vaccutainers. After collection, the tubes were kept undisturbed for 90 min and the ensuing serum separated from blood clot by centrifuging at 2500 rpm for 5 min.
Serum samples were stored at−20º C till the time of ECP assay.
After the histopathology results were available, the stored sera from 18 continuous cases of acute appendicitis and 6 cases of normal appendix were assayed for ECP.
All appendicectomy specimens were formalin fixed and three cross sections were taken representing the base, middle and tip. Sections were routinely processed and stained with hemotoxylin and eosin (H&E). Eosinophils were counted in the muscle layer and expressed as number of cells per high-power field. The cases were classified as:
Acute appendicitisAppendix within normal histological limits
Eosinophilic chemotactic protein assay
Eosinophil cationic protein levels were estimated by chemiluminescence assay in IMMULITE fully automated analyzer as per manufacturer's instructions. 
Serum ECP levels in the different categories are shown in [Table 1]. The total leukocyte counts and absolute eosinophil counts (calculated from TLC and differential counts) in acute appendicitis (10.8 × 10 9 /L and 0.25 × 10 9 /L) did not statistically differ from cases with normal appendix (10.7 × 10 9 /L and 0.46 × 10 9 /L).
The relationship of ECP levels with the duration pain in cases of acute appendicitis is shown in [Figure 1]. The duration of pain is the time between onset of pain and collection of the blood sample.
The mean eosinophil counts were 16.6/hpf in cases of acute appendicitis and 1.2/hpf in normal appendices ( P = 0.0003; Kruskall-Wallis test). There was no significant relation between the degree of mural eosinophil infiltration and serum ECP by linear regression ( r 2 = 0.19; P = 0.073).
The mean serum ECP levels in acute appendicitis in this study (45.3 µg/L; 95% CI 27.7-63.0) was significantly above that of serum ECP in healthy volunteers (13.2 µg/L; 95% CI 8.3-18.1; P = 0.007; Kruskall-Wallis test). Mean serum ECP was higher in acute appendicitis than in asthma and in cases of elective appendicectomies where the histology was normal. However, these were not statistically significant, most likely because the numbers of asthma (3) and normal appendix (6) were small. Admittedly, the number of controls was small, but the mean value in healthy volunteers agreed well with the manufacturer's value (11 g/L) and despite the low numbers the difference between appendicitis and normal volunteers was significant.
The material for the study was collected in a period of less than 1 month and all the sera were stored at −20ºC in the same conditions. The effects of temperature and time on serum ECP levels  were thus same for all the specimens.
Raised serum ECP levels are seen in conditions characterized by tissue eosinophil infiltration and activation. Fairly widespread degranulation of tissue eosinophils must be necessary to produce elevation of ECP in the serum. Acute asthmatic attack is an example wherein eosinophil infiltration occurs along the entire bronchial tree. In acute asthma exacerbations, the mean serum ECP levels reported in different studies vary from 23.2 g/L to 41.7 g/L. ,,, The mean ECP level in this study is comparable or even more than this.
It has been suggested that eosinophilic infiltrate in the appendix may be a reflection of a resolving or regression phase of acute appendicitis.  But our cases of acute appendicits were all of short duration in which an emergency appendicectomy was performed. Further, all of them showed acute inflammation involving the muscle layer.
The whole cross-sectional area of the appendix is far smaller when compared to the total cross-sectional area of the bronchial tree. To produce serum ECP levels comparable to acute asthmatic attacks, more widespread eosinophil infiltration and activation than that accounted by the appendix is probably required. Is it possible then that the initial pathogenic lesions of acute appendicitis are not limited to the appendix, but more generalized to say the ileocecal area? Aravindan had in fact suggested this possibility in his article because of a case in which a segment of ileum resected along with the appendix because of narrowing, showed mural eosinophil infiltration.  In this scenario, why is it that the appendix becomes the sole target of acute inflammation? The obvious explanation is that the appendix is highly vulnerable due to its small size to accumulating edema fluid compromising mucosal blood supply - something that would not happen in the rest of the bowel.
There is no correlation between the peripheral blood eosinophil counts and the serum ECP levels. Only 3 out of 18 cases of acute appendicitis has counts of 8% or more. None of the patients had history of atopy. This is in contrast to eosinophilic gastroenteritis in which about half have atopy and three-fourths, peripheral blood eosinophilia.  The early pathogenesis of acute appendicitis must therefore be qualitatively different from eosinophilic gastroenteritis and seems to be a local phenomenon unassociated with generalized allergy.
Eighty-three percent of the cases of acute appendicitis had serum ECP values above 18.8 g/L - the upper range value for normal volunteers. Only 55.5% had values above 30 g/L. The cases with low values also had classical histology of acute appendicitis. Explanation for these cases has to be sought for the allergic hypothesis to be viable. Two possibilities come to mind.
As mentioned earlier, early changes may involve bowel regions beyond the appendix. The cases with lower serum ECP may be the ones with lesser area of involvement.It is possible that serum ECP levels fall after the initial rise. The relation of ECP levels to the duration of illness (from start of pain to time of surgery in hours) shown in [Figure 1] seems to bear this out. Though not statistically significant, there is an inverse relation between serum ECP level and duration of illness.
Some cases of appendicectomies with normal histology show overlap of values with acute appendicitis. Recurrent appendicitis occurs in about 6.5-11% all cases of appendicitis. , It is possible to think of recurrent appendicitis as something analogous to chronic asthma, or atopy limited to the gastrointestinal tract, wherein continuous IgE production and mast cell activation occur, leading to multiple acute episodes. Low-level ECP elevations may be present in such patients in between acute attacks.
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