The p53 tumor suppressor protein is an important regulator of cell proliferation 
and apoptosis. p53 can be found in the nucleus and in the cytosol, and the 
subcellular location is key to control p53 function. In this work, we found that 
a widely used monoclonal antibody against p53, termed Pab 1801 (Pan antibody 
1801) yields a remarkable punctate signal in the cytoplasm of several cell lines 
of human origin. Surprisingly, these puncta were also observed in two 
independent p53-null cell lines. Moreover, the foci stained with the Pab 1801 
were present in rat cells, although Pab 1801 recognizes an epitope that is not 
conserved in rodent p53. In contrast, the Pab 1801 nuclear staining corresponded 
to genuine p53, as it was upregulated by p53-stimulating drugs and absent in 
p53-null cells. We identified the Pab 1801 cytoplasmic puncta as P Bodies (PBs), 
which are involved in mRNA regulation. We found that, in several cell lines, 
including U2OS, WI38, SK-N-SH and HCT116, the Pab 1801 puncta strictly 
colocalize with PBs identified with specific antibodies against the PB 
components Hedls, Dcp1a, Xrn1 or Rck/p54. PBs are highly dynamic and 
accordingly, the Pab 1801 puncta vanished when PBs dissolved upon treatment with 
cycloheximide, a drug that causes polysome stabilization and PB disruption. In 
addition, the knockdown of specific PB components that affect PB integrity 
simultaneously caused PB dissolution and the disappearance of the Pab 1801 
puncta. Our results reveal a strong cross-reactivity of the Pab 1801 with 
unknown PB component(s). This was observed upon distinct immunostaining 
protocols, thus meaning a major limitation on the use of this antibody for p53 
imaging in the cytoplasm of most cell types of human or rodent origin.