Adult Aged Apoptosis Apoptotic cell clearance Case-Control Studies Cytophagocytosis Gene Expression Regulation Humans Lipopolysaccharides Middle Aged Monocytes Receptors, Vasoactive Intestinal Peptide Receptors, Vasoactive Intestinal Peptide, Type II Sjoegren syndrome Sjogren's Syndrome Sjögren's syndrome patients VPAC receptors Vasoactive Intestinal Peptide Young Adult adult aged apoptosis apoptotic cell clearance article cell function cell isolation cell phagocytosis clinical article controlled study epithelium cell