β1 integrin also serves as a coreceptor for entry of wild-type human parvovirus B19 in PMA-treated K562 cells. Southern blot analysis of low M_r DNA isolated from undifferentiated (lanes 1-2) and PMA-differentiated (lanes 3-6) K562 revealed the presence of internalized single-stranded (ss) wt parvovirus B19 genomes only in PMA-treated cells (lane 3). Both parvovirus B19 anti-VP2 antibodies (lane 4) and inhibitory β1 integrin antibodies (lane 5) abolished it, whereas β1 integrin-activating antibody increased viral entry (lane 6). Southern blot analyses were performed as described in “Materials and methods.”