Aim of the study:
To determine the interaction of components of complement C3 and C4 with indicators of unspecific immune system and biological inflammatory markers.

Material and methods:
A total of 80 children were recruited, including 60 patients with Henoch-Schönlein purpura (HSP) aged from 2 to 17 years old and 20 healthy children of the same age. The HSP patients were divided into two groups: an HSPWN group (n = 47), including HSP patients without renal involvement; and an HSPN group (n = 13), including patients with HSP combined with renal syndrome. The control group comprised 20 healthy children. Standard tests, clinical examination, and measurement of the levels of C3 and C4 complement fractions were performed on admission and during remission time. The components of the complement system C3 and C4 were determined by ELISA using standard ELISA C3 and C4 kits from AssayPro, USA.

Results:
It was significantly proved the difference between medians in all groups due to high criteria H for C3 in acute and remission periods (H = 15.58, p = 0.000 and H = 14.58, p = 0.00, respectively). The serum level of C3 was significantly decreased in patients of HSPWN and HSPN groups in the acute period (pHSPWN-C = 0.000, pHSPN-C = 0.004) and during remission (pHSPWN-C = 0.000, pHSPN-C = 0.018), compared with controls. The serum level of C4 was significantly decreased in patients in the HSPWN group in the acute period compared with patients on the HSPN group (pHSPWN-HSPN = 0.020). The level of C4 was significantly lower during remission time in both groups (T = 144.0, p = 0.041 and T = 10.5, p = 0.025, respectively).

Conclusions:
Abnormalities of the complement system in HSP have been reported. Hypocomplementaemia was not dependent on the severity of the process of HSP. In the period of remission, the levels of C3 and C4 approached the control group’s values.