Campylobacter jejuni is a common cause of human gastrointestinal disease wo
rldwide. Despite the prevalence of C. jejuni infections, the mechanisms of
C. jejuni pathogenesis remain ill-defined. Invasion of the cells lining the
intestinal tract is hypothesized to be essential for the development of C.
jejuni-mediated enteritis. Recent studies in our laboratory have revealed
that C. jejuni secrete proteins, termed Cia for Campylobacter invasion anti
gens, upon incubation with human intestinal cells. A mutation in one of the
genes encoding a secreted protein resulted in an invasion-deficient phenot
ype. The purpose of this study was to identify a component capable of stimu
lating the synthesis and secretion of the Cia proteins from C. jejuni. Here
, we report that these processes can be induced upon incubating C. jejuni i
n medium supplemented with fetal bovine serum. The synthesis and secretion
of the Cia proteins were not affected by heat-treatment of the fetal bovine
serum, indicating that the stimulating molecule in serum is heat stable. T
he stimulatory molecule was not unique to fetal bovine serum as sera from o
ther sources including human, pig, sheep, goat, rabbit, mouse, and chicken
also induced the synthesis and release of the Cia proteins. These findings
indicate that the synthesis and secretion of the Cia proteins can be induce
d in a cell-free system by incubating C, jejuni in serum-supplemented tissu
e culture medium.