Acute Cellular Rejection - Grade 0R
Morphologically, acute cellular rejection consists of a mononuclear inflammatory infiltrate that is predominantly a T-cell mediated response directed against the cardiac allograft. In severe cases, there is also participation of granulocytes in the rejection process. B cell infiltrates are rarely present in mild rejection. However, a substantial increase in activated B lymphocytes and NK cells are seen in moderate rejection, suggesting their important role as promoters and effectors of cellular rejection.
The absence of cellular rejection is called Grade 0R and and example is shown below.
In Grade 0 R there is no evidence of mononuclear
(lymphocytes / macrophages) inflammation or myocyte
damage. 
