Perianal fistula significantly impacts patients' quality of life, causing perineal pain, foul-smelling discharge, and sometimes incontinence. Approximately 90% of perianal fistulas are of the cryptoglandular type. Crohn's disease is the second most common cause. Few studies have compared the immune cell composition in these types of fistulas, suggesting different cellular pathogenesis.

This was a case-control, basic science study. Patients with both Crohn's disease and cryptoglandular fistula were selected, matched for age and sex. Exclusion criteria included active gastrointestinal infection, active perianal abscess, malignancy, and other autoimmune diseases such as lupus and rheumatoid arthritis. Patients from both groups were selected from those attending the gastroenterology clinic at Imam Hospital. Peripheral blood samples were sent to the immunology laboratory. In the first step, the white blood cell count in the peripheral blood was determined. Subsequently, mononuclear cells were extracted and the frequency of cells was analyzed using flow cytometry based on the expression of CD3, CD4, CD8, CD38, and HLA-DR markers.

Twenty-one patients were enrolled in the study, of whom 11 had cryptoglandular fistulas and 10 had Crohn's disease. The mean age of patients in the Crohn's group was 36.1 ± 16.8 years and in the cryptoglandular group was 43.7 ± 13.2 years (P-value=0.26). The mean disease duration was 5.9 years with a standard deviation of 5.15 in the Crohn's group and 6.8 years with a standard deviation of 8.9 in the other group (P-value=0.185). The percentage of female patients in the intervention group was 54.2%, which was 55.6% in the control group (P-value=1). Results showed that the percentage of CD3+, CD4+, and HLA-DR+ cells did not differ significantly between the two groups. However, CD8+, CD3+CD8+, CD3+CD8+CD38+, and CD3+CD38+ cells were significantly higher in the Crohn's group compared to the cryptoglandular group. There was also no significant difference in the frequency of CD3+HLA-DR+ cells between the two groups (P>0.05).

This study showed that the frequency of CD3+CD38+CD8+ cells can be used to diagnose and differentiate perianal fistulas caused by Crohn's disease from cryptoglandular fistulas. Furthermore, these cells may be potential therapeutic targets for patients with Crohn's disease.