Abstract. Plasmalemmal caveolae are a membrane specialization that mediates transcytosis across endothelial cells and the uptake of small molecules and ions by both epithelial and connective tissue cells. Recent findings suggest that caveolae may, in addition, be involved in signal transduction. To better understand the molecular composition of this membrane specialization, we have developed a biochemical method for purifying caveolae from chicken smooth muscle cells. Biochemical and morphological markers indicate that we can obtain ~1.5 mg of protein in the caveolae fraction from •100 g of chicken gizzard. Gel electrophoresis shows that there are more than 30 proteins enriched in caveolae relative to the plasma membrane. Among these proteins are: caveolin, a structural molecule of the caveolae coat; multiple, glycosylphosphatidylinositol-anchored membrane proteins; both G~ and Ga subunits of heterotrimeric GTP-binding protein; and the Ras-related GTP-binding protein, RaplA/B. The method we have developed will facilitate future studies on the structure and function of caveolae.T HF.RE is increasing evidence that plasmalemmal caveolae are a membrane specialization capable of sealing off from the extracellular environment to create a unique, membrane bound compartment at the cell surface. The dynamics of caveolae opening and closing is best observed in endothelial cells (46,47), where they appear to form plasmalemmal vesicles that move across the cell and fuse with the abluminal membrane. Each round of caveolaemediated transcytosis transports a portion of molecules from the blood to the tissue space without merging with other endocytic pathways. Although in other cell types the budding event has not been seen with the electron microscope, biochemical studies have shown (1%19) that caveolae can sequester membrane bound ligands away from the extracellular space and facilitate their delivery to the cytoplasm of the cell. This process is called potocytosis (3).What distinguishes potocytosis from other endocytic pathways is the use of glycosylphosphatidylinositol (GPI) 1-anchored membrane proteins to concentrate low molecular weight molecules and ions in closed caveolae (22,41). Morphological (54) and biochemical (5, 7) methods have

Abstract. The folate receptor is clustered on the surface of MA104 cells in association with caveolae. This relationship is thought to be essential for the proper internalization and recycling of the receptor during the delivery of 5-methyltetrahydrofolate to the cytoplasm of folate-depleted cells. Both the clustered organization of the receptor and the integrity of caveolae are disrupted when cells are deprived of cholesterol. We now show that cholesterol depletion of MA104 cells markedly reduces the rate of 5-methyltetrahydrofolate internalization and causes a 70% decline in the number of receptors present in the internal, recycling compartment. This effect is consistent with morphologic data showing that cholesterol-depleted MA104 cells have a reduced number of caveolae as well as fewer receptors per caveolae.

Humoral immunity against Streptococcus mutans infection was analyzed in caries‐active and caries‐free young adults by immunoblotting. All volunteers from both groups had detectable salivary immunoglobulin A (IgA) and serum IgG antibodies, with similar profiles. They could be classified on the basis of relative intensity of the immunoblot bands into categories of high or low responders. Common protein antigens with molecular weight ranging from approximately 45 to 190 kDa could be found either extracellularly or associated with the cell wall of S. mutans cultured in vitro. The predominant reactive antigens recognized by both IgA and IgG were of proteins around 63 and 60 kDa. Detection of IgA antibodies to the various antigens of S. mutans in individual saliva samples did not always correlate with serum IgG antibody profiles. In addition, distinct bands, which reacted preferentially with either IgA or IgG, could be detected by antibodies from specific subjects. Differential reactivities of salivary IgA and serum IgG antibodies to two, cell‐wall associated protein antigens around 33 and 36 kDa were found in caries‐active and caries‐free young adults; 30.8% of caries‐free subjects and 12% of caries‐active subjects (P<0.01) exhibited detectable antibody response to these antigens. This difference was not attributable to variations in antibody levels, since antibody response to these proteins were still detectable in some caries‐free but not caries‐active individuals whose levels of antibodies to other antigens were low. Thus, a new antibody profile which correlates with dental caries disease activity has been identified in a selected population. Differences in mucosal and systemic immune responses to S. mutans seem to be both antigen and host dependent.