Morphological characterization of the malignant B lymphocytes in the bone marrow and blood of patient MZL-1. (A,B) Immunohistochemical analysis of bone marrow biopsies. Sections were stained with anti-CD79a [Ig-] (A) and anti-DBA.44 (B) antibodies. Both antibodies stained lymphoid cells that were predominantly located within the sinusoids of the bone marrow. The sinusoids are indicated by arrowheads (cross-section) or arrows (oblique [A] and longitudinal [B] sections), respectively. The clear spheroidal areas are occupied by fat cells. (C) Staining of CD5⁺CD19⁺peripheral blood cells. CD5⁺CD19⁺ cells were sorted from mononuclear cells of the peripheral blood and stained with the anti-DBA.44 antibody.25 About 70% of all sorted cells were strongly positive for the DBA.44 antigen. (D) Morphology of the malignant B lymphocytes. Blood smears of patient MZL-1 were analyzed by the modified Wright staining. Four representative B cells are shown at high magnification together with adjacent erythrocytes. These B cells contain a round or ovoid nucleus that is surrounded by a moderately increased amount of basophilic cytoplasm. Most malignant B cells have the appearance of villous lymphocytes as evidenced by the presence of cytoplasmic projections or short thin villi, which are often asymmetrically located on one side of the cell.