Activated WASP⁻ B lymphocytes express short microvilli.

B cells from WASP⁻ and WASP⁺ mice were cultured for 48 hours with indicated stimuli, gently resuspended, then fixed and prepared for transmission electron microscopy. Note the extensive network of microvilli in cell contacts of anti-CD40 plus IL-4–stimulated cells, especially pronounced in WASP⁺cells. These observations are representative of 2 similar experiments. Size bar represents 1 μm. Original magnification 3800 × (LPS) and 3000 × (anti-CD40 plus IL-4).