The invention provides isolated nucleic acids molecules, designated BBAP nucleic acid molecules, which encode proteins that interact with or bind to BAL molecules, which are differentially expressed in non-Hodgkin's lymphoma. The invention also provides antisense nucleic acid molecules, recombinant expression vectors containing BBAP nucleic acid molecules, host cells into which the expression vectors have been introduced, and non-human transgenic animals in which a BBAP gene has been introduced or disrupted. The invention still further provides isolated BBAP proteins, fusion proteins, antigenic peptides and anti-BBAP antibodies. Diagnostic methods using compositions of the invention are also provided.