The process in which an antigen-presenting cell expresses antigen (peptide or lipid) on its cell surface in association with an MHC protein complex. [ GOC:add http://purl.obolibrary.org/obo/go/references/0000022 http://www.ncbi.nlm.nih.gov/pubmed/15771591 http://www.ncbi.nlm.nih.gov/pubmed/15928678 http://openisbn.com/search.php?q=0781735149&isbn=1/ ]