Homodimeric Granzyme A opsonizes Mycobacterium tuberculosis and inhibits its intracellular growth in human monocytes via TLR4 and CD14.

Mycobacterium tuberculosis (Mtb)-specific γ9δ2 T cells secrete GzmA protective against intracellular Mtb growth. However, GzmA enzymatic activity is unnecessary for pathogen inhibition and the mechanisms of GzmA-mediated protection remain unknown. We show GzmA homodimerization is essential for opsonization of mycobacteria, altered uptake into human monocytes and subsequent pathogen clearance within the phagolysosome. While monomeric and homodimeric GzmA bind mycobacteria, only homodimers also bind CD14 and TLR4. Without access to surface expressed CD14 and TLR4, GzmA fails to inhibit intracellular Mtb. Upregulation of Rab11FIP1, was associated with inhibitory activity. Further, GzmA colocalized with and was regulated by protein disulfide isomerase (PDI)A1, which cleaves GzmA homodimers into monomers and prevents Mtb inhibitory activity. These studies identify previously unrecognized role for homodimeric GzmA structure in opsonization, phagocytosis and elimination of Mtb in human monocytes, and highlights PDIA1 as a potential host-directed therapy for prevention and treatment of tuberculosis, a major human disease.