Background: Acute cellular heart transplant rejection is characterized by active lymphocytic infi ltration, whereas the humoral response presents the complement deposits in myocardial tissue. These two processes may be responsible for hemodynamic compromise in the first months after heart transplantation, when cellular rejection becomes faster and more severe than humoral rejection. The specific character of the first biopsy, because of the summarized nociceptive factors (e.g. rejection, warm ischemia, transportation time) should be pointed out. The aim of the study was to estimate the coexistence of humoral rejection in the first post-transplant biopsy with moderate cellular rejection, as an additional prognostic factor.
Material/Methods: A part of the first post-transplant endomyocardial biopsy
material was collected in a tissue freezing medium, whereas the remaining part was used for routine histology studies. The studied group included 13 biopsies (obtained from 11 men and 2 women; mean age 52.6±5.3 yr) with verified ISHLT mild/moderate rejection grade, whereas control group consisted of 11 biopsies (obtained from 8 men and 3 women; mean age 54.8±3.6 yr) with no signs of rejection. The complement deposits were determined immunohistochemically using anti-C4d antibodies (Quidel Corporation).
Results: None of the control group cases showed positive reaction, whereas in the studied group in 3 cases (3 men; 56.1±5.8 yr) the cellular infiltrates joined with regional positive anti-C4d expression. This expression occurred in all myocardial components adjacent to lymphocytic infiltrations. Survival rate was comparable in both clear cellular and mixed rejections. Relative rate of grade 3 rejection in post-transplant period was increased in patients with mixed rejection.
Conclusions: The term "mixed acute rejection" should be applied for such cases, when there is coincidence of the two forms of acute rejection and it seems to be associated with more frequent grade 3 rejection in the long term follow up.

Keywords: Heart Transplantation