Expression of laminin  polypeptides in newborn mouse bone marrow. Immunostaining with an antiserum reacting with laminin 1, β1, and γ1 chains (a) shows widespread expression of some of these chains in the arteriolar walls (arrow), in the sinusoids, and in the intersinusoidal spaces, as shown by a double immunofluorescence with MECA-32 to stain endothelial cells in the sinusoids and in the arteriole (arrow) (b). Antibodies 4G6 reacting with laminin 5 polypeptide (d) and 8G11-D10 recognizing laminin 2 chain (f) and show a reaction in some arterioles. Laminin 1 chain, identified with MoAb 198, (e) is not expressed in the newborn bone marrow. Control staining (c) with nonimmune rabbit serum (NRS) is negative. Laminin polypeptide chains detected by each antiserum or antibody are indicated in the lower left corners of the figures.