A po I i pop rote i n B-1 00: i m m u no I oca1 izat i on and synthesis in human intestinal mucosa

Despite the evidence that the human small intestine produces two separate species of apoB mRNA encoding for B-100 and B-48, there is a paucity of data concerning the expression of the latter form in this organ. Using a high resolution immunopld approach, withspecific polydonal antibodies and a panel dmonadonal antibodies (ZD8, 3Al0, 4G3), both forms of apoB (B-48 and B-100) were revealed over entemcytes of pediatric intestinal samples. Intense labeling was observed over microvilli, apical smooth membrane vesicles, multivesicular bodies, the basolateral membrane, as well as the tmm Golgi region. Only low labeling was found over the rough endoplasmic reticulum (rER). Similar patterns of apoB distribution characterized both duodenal and jejunal regions. The presence of labeling over the Golgi apparatus and rER suggests a synthetic activity of both forms of apoB by the epithelial cells. To test this hypDthesis human in& was incubated with (sH)leucine, homogenized, and subjected to immunoprecipitation for apoB. Immunoprecipitates contained radioactivity mainly in apoB-48 with relatively small amounts in apoB-100 when examined by NaDodSO,-polyacrylamide gel electrophoresis. These findings were further supported by the biochemical determination of apoB-100 and apoB-48 in chylomicron particles isolated from thoracic duct lymph of a human donor. Taken together, our data suggest that the human intestine is able to synthesize and to express the apoB-100. -Levy, E., C. Rochette, I. Londono, C.C. ROY, R.W. Milne, Y.L. Marcel, and M. Bendayan. Apolipoprotein B-100: immunolocalization and synthesis in human intestinal mucosa. J. Lipid Res. 1990. 31: 1937-1946.