sentences:  Lewis antigen is often decreased on RBCs during pregnancy with some women transiently typing as Le(a-b-).This is thought to be due in part to increased circulating plasma volume in pregnancy and increased lipoprotein.The Le(b) and H antigens are receptors for the bacteria "Helicobacter pylori", a gram-negative bacterium that can cause gastritis and has been implicated in peptic ulcer disease, gastric adenocarcinoma, mucosa-associated lymphoma (or mucosal associated lymphatic tissue lymphoma – MALToma) and idiopathic thrombocytopenic purpura (ITP).