CRP-
ductin is a
protein expressed mainly by mucosal epithelial cells in the mouse. Sequence homologies indicate that CRP-
ductin is the mouse homologue of human
gp-340, a
glycoprotein that agglutinates microorganisms and binds the lung mucosal
collectin surfactant protein-D (
SP-D). Here we report that purified CRP-
ductin binds human
SP-D in a
calcium-dependent manner and that the binding is not inhibited by
maltose. The same properties have previously been observed for
gp-340 binding of
SP-D. CRP-
ductin also showed
calcium-dependent binding to both gram-positive and -negative bacteria. A polyclonal antibody raised against
gp-340 reacted specifically with CRP-
ductin in Western blots. Immunoreactivity to CRP-
ductin was found in the exocrine pancreas, in epithelial cells throughout the gastrointestinal tract and in the parotid ducts. A panel of
RNA preparations from mouse tissues was screened for CRP-
ductin and
SP-D expression by reverse transcription-PCR. The pancreas was the main site of synthesis of CRP-
ductin, but transcripts were also readily amplified from salivary gland, the gastrointestinal tract, liver, testis, uterus and lung. Lung was the main site of synthesis of
SP-D, but transcripts were also amplified from uterus, salivary gland, thymus, thyroid gland, pancreas and testis. We conclude that CRP-
ductin is the mouse homologue of human
gp-340 and that its capacity to bind
SP-D as well as gram-negative and gram-positive bacteria suggests a role in mucosal immune defense.