What causes atypical mononuclear cells in peripheral blood?

Atypical mononuclear cells in peripheral blood can be caused by various factors, including viral infections (such as Epstein-Barr virus), autoimmune disorders, and hematologic malignancies. These cells often indicate an immune response, typically in reaction to infections or inflammation. In some cases, they may also arise from reactive processes or chronic conditions. A thorough clinical evaluation is necessary to determine the underlying cause.