Introduction:
The association between serum soluble apoptotic markers, eosinophil cationic protein (ECP), and inflammatory parameters in allergic diseases has seldom been studied. This study aimed to investigate apoptotic activity in allergic diseases and its relationship with ECP, systemic inflammation, and severity of atopic sensitisation.

Material and methods:
A total of 125 patients with allergic diseases were investigated by measuring ECP, APO-1, tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), allergen-specific immunoglobulin E (sIgE), total IgE (tIgE), and high-sensitivity C-reactive protein (hsCRP) levels.

Results:
ECP, APO-1, TRAIL, and hsCRP levels were significantly higher in patients with allergic diseases than in healthy individuals. Patients who tested positive for ECP had no significant differences in APO-1 and TRAIL levels compared with those who tested negative for ECP. However, among the patients who tested positive for ECP, those with elevated hsCRP concentrations had significantly higher APO-1 and TRAIL levels than those without elevated hsCRP concentrations (p < 0.001, respectively). APO-1, TRAIL, and ECP levels were significantly higher in patients with inhalant allergy than in those with food allergy. APO-1 and TRAIL were significantly associated with hsCRP but not with tIgE and sIgE scores.

Conclusions:
Apoptotic activity is enhanced in allergic diseases and is more closely linked to concomitant systemic inflammation than to the severity of atopic sensitisation, particularly in patients with inhalant allergy.