A Mott cell is a mature plasma cell that produces an excessive amount of immunoglobulins. These (defective) antibodies accumulate, creating so-called "Russel bodies"; a clustering of large, white cytoplasmic inclusions.

Mott cells can occur in both benign and malignant diseases (e.g., infections and multiple myeloma). The inclusions should not be confused with Burkitt Lymphoma, in which the lymphocytes involved are much younger and the inclusions are often like a string of pearls around the nucleus.