BAK1 and infection: Given that bak expression was elevated over the time course of infection by H. felis in the murine gastric mucosa within 2 wk and returned to baseline levels of expression at 6–20 wk following infection, and that there was an expanded proliferative compartment in the gastric corpus of untreated bak-null mice, we determined how bak-null mice responded to both short (6 wk)- and long (48 wk)-term infections with H. felis.