An intracellular pathway is required for ABA-tyrosine presentation to T cells.

Although tyrosine-azobenzenearsonate (ABA-Tyr) is not degraded by proteolytic enzymes, its presentation by accessory cells is inhibited by lysosomotropic agents such as chloroquine. Presentation of ABA-poly-L-glutamic, alanine, tyrosine (ABA-GAT) is similarly inhibited by chloroquine, but in contrast to ABA-Tyr it is also inhibited by leupeptin. Finally formaldehyde fixation of accessory cells after pulsing with ABA-Tyr but not before permits successful stimulation of ABA-specific hybridoma cells. These results suggest that a lysosomal pathway but not digestion is necessary for the association of ABA-Tyr and la molecules for presentation.