Effect of antibiotic pretreatment on immunogenicity of human heart valves and component cells

Background. For many years valves have been sterilized with high-dose antibiotics before implantation, but now there is an increasing trend to using “homovital” valves, which have been exposed to very low dose antibiotics. Methods. To investigate the immunogenicity of valve tissue, before and after exposure to high- and low-dose antibiotics, peripheral blood mononuclear cells and human allogenic T cells were cocultured with antibiotic-treated valve discs, cultured valve endothelial cells, and fibroblasts. Proliferation was measured by uptake of thymidine labeled with hydrogen 3. Results. Untreated tissue pieces stimulate peripheral blood mononuclear cells (4,080 ± 980 cpm) at day 0 with similar results after 1 day in Hank’s balanced salt solution (4,272.4 ± 1,307 cpm) reducing to 2,442 ± 926 cpm after 3 days and 1,111 ± 255 cpm after 5 days; antibiotic-treated pieces are less immunogenic after 1 (2,560 ± 403 cpm), 3 (1,550 ± 60 cpm), 5 (717 ± 295 cpm), and 7 days (633 ± 174 cpm) in homovital solution, whereas sterilized pieces are not immunogenic (184 ± 96 cpm) after only 1 day in strong antibiotics. Histologic analysis showed that this corresponds to a reduction of class I and class II expression by human valve endothelial cells. Human valve endothelial cells but not fibroblasts are capable of causing direct stimulation of CD4+ T cells. However, human valve endothelial cells poorly stimulate CD4+ T cells after incubation in homovital solution for 24 hours. Conclusions. This study shows that valve tissue is immunogenic and this immunogenicity is mediated mainly by endothelial cells. However, the immunostimulatory potential of the valve can be reduced by incubating the solution in an antibiotic cocktail.