Nucleic acids encoding CD100 molecules

Isolated nucleic acid molecules encoding novel CD100 molecules which stimulate a leukocyte response, such as a B cell response, including B cell aggregation, B cell differentiation, B cell survival, and/or T cell proliferation are disclosed. These novel molecules have a certain homology to semaphorins, proteins which are growth cone guidance molecules that are critical for guiding growing axons of neurons to their targets. In addition to isolated nucleic acids molecules, antisense nucleic acid molecules, recombinant expression vectors containing a nucleic acid molecule of the invention, host cells into which the expression vectors have been introduced are also described. The invention further provides isolated CD100 proteins, fusion proteins and active fragments thereof. Diagnostic and therapeutic methods utilizing compositions of the invention are also provided.