CD28 and histiocytic sarcoma: In addition, some inflammatory markers, such as fibrinogen, ferritin, and C-reactive protein, have been reported to be increased in the serum of dogs with histiocytic sarcoma [13–15], and the expression of CD28, CTLA-4, and PD-1 is affected by a systemic inflammation induced by various neoplastic, infectious, and autoimmune diseases [10, 16–18].