Objective:
The aim of the study was to analyze the concentrations of some serological parameters in patients undergoing antibiotic therapy for LD, and to assess the potential use of IgG anti-C6VlsE in the assessment of treatment effectiveness.

Material and methods:
The study involved 21 patients diagnosed with LD. To determine the levels of anti-C6VlsE IgG, metalloproteinases and cytokines, blood was collected three times: before treatment, immediately after treatment, and 3–4 months after treatment.

Results:
Immediately after the antibiotic therapy, all the patients in the study group declared improvement in their health. At 3–4 months post-treatment, 50% of patients reported recurrence of the disease symptoms. The anti-C6VlsE IgG concentrations at the analyzed time points exhibited varied dynamics: in 15% of patients, a decrease in the concentration of anti-C6VlsE was observed in the three consecutive serum samples; an increase of anti-C6VlsE IgG was detected in 35% of cases; in 15% of the subjects, the concentration of anti-C6VlsE IgG increased immediately after the antibiotic therapy and declined after 3–4 months, whereas a reverse situation was noted in 10% of the patients.

Conclusions:
The presence of high concentrations of anti-C6VlsE IgG is associated with appearance of response to Borreliella spp. infection, which suggests that the parameter can be used in the diagnosis of the active form of borreliosis. However, from a practical point of view, a marker of successful elimination of infection should indicate the effectiveness or failure of antibiotic therapy within a relatively short post-treatment period. The anti-C6VlsE IgG antibodies do not seem to satisfy this provision.