The interaction between macrophage and Mycobacterium avium subsp. paratuberculosis (MAP) was found to be complex processes involving survival or death of macrophage with bacterial persistence or clearance depending upon the number of bacteria infected per macrophage (multiplicity of infection, MOI). The bovine strain of MAP (C-123/IVRI) isolated from clinically infected cattle was found to be ingested by bovine blood monocyte-derived macrophages, multiplied within them, and resulted in differential expression of a number of pro-inflammatory cytokine genes and induction of macrophage apoptosis. At MOI>1, MAP was found to be not harmful for macrophages and down-regulated most of the pro-inflammatory genes. The maximum apoptotic index was found to be 2-3% at 24 h post-infection, which was as low as baseline apoptosis observed in uninfected control cells. MAP at MOI>10 induced apoptosis in 5% of macrophages at 6 h, 8 % at 12 h, and 13% at 24 h post-infection. A number of pro-inflammatory genes were down-regulated during this condition with activation of caspase-dependent and mitochondrial pathways of apoptosis. On the other hand, MAP at MOI>50 or 100 was found to be potentially cytotoxic for macrophages. MAP at MOI>50 induced apoptosis in 20, 29 and 34% of macrophages at 6, 12 and 24 h, respectively. Down-regulation of pro-inflammatory cytokines as well as activation of caspase-independent and NO-dependent pathways of apoptosis was observed in these conditions. The results of the present study suggest that interaction of MAP with macrophage is a complex process with activation of caspase-pathway dichotomously depending upon the multiplicity of infection.