The antibody LN2 recognizes an extracellular epitope of CD74 (the MHC II-associated invariant chain, Ii), a type II transmembrane protein expressed in antigen-presenting cells, as well as e.g. on activated neoplastic cells in T cell lymphomas, in lymph node germinal center, mantle zone B cells, histiocytes, interdigitating reticulum cells, Langerhans cells, thymic dendritic cells and peripheral blood B lymphocytes.