Figure 4. IMCs derived histamine protects against the apoptosis of cardiomyocytes.

H9c2 cells were co-cultured with CD11b⁺Gr-1⁺ IMCs isolated from HDC^−/− or WT mice and H₂O₂ (100 μmol/L) was added to induce oxidative stress. After 48 hrs, Annexin V-PI staining was performed to detect apoptosis, H9c2 cells were distinguished from IMCs by anti-CD11b. (a) FACS data showed IMCs from both groups were equally sensitive to H₂O₂ (n = 4). (b) FACS analysis showed the increases of both early and late apoptosis of H9c2 cells co-cultured with HDC^−/− IMCs (*p < 0.05 vs WT; n = 4). These effects could be abrogated by exogenous addition of histamine (5*10⁻⁵M) (*p < 0.05 vs HDC^−/−, **p < 0.01 vs HDC^−/−; n = 4). (c), Exogenous addition of histamine alone could increase the apoptosis of H9c2 cells (**p < 0.01 vs control; n = 3).