Paradigm redux—Mycobacterium avium subspecies paratuberculosis-macrophage interactions show clear variations between bovine and human physiological body temperatures

The physiological conditions encountered by pathogenic mycobacteria inside their hosts significantly influence their adaptation, virulence, and gene expression. Current in vitro models investigating host-pathogen interactions of Mycobacterium avium subsp. paratuberculosis use 37 °C, the normal body temperatures of mice and humans. However since the physiological temperature of MAP's natural host is 39 °C, we hypothesized that host and pathogen behavior to vary considerably in comparison to 37 °C. Our MAP-macrophage interaction studies show striking differences in regards to velocity of cell invasion of MAP as well as bacterial and host gene regulation at 39 °C compared with 37 °C. Upregulation of host genes (nod2, tlr2, mapkp38 and il-10) follow a similar trend at 37 °C and 39 °C; however, there is over a five-fold increase as early as 0.5 and 2 h in 39 °C treatments. While host signaling is completed by 48 h p.i. at 39 °C in MDMs cultures due to early cell death, signaling and infection is sustained at 37 °C. Surprisingly, transcription of MAP genes did not show a set pattern and were upregulated at different time points for both temperatures. Interestingly, MAP genes encoding a lipase (lipN) and an oxidoreductase (MAP3464) are staggered at 39 °C, while they increase steadily at 37 °C. In conclusion, infection and culture at a physiologically relevant temperature influences host-pathogen interaction, which may have far reaching ramifications including for currently used animal models, in vitro culture methods, bacterial pathogenesis and host responses, and vaccine candidate design and screening.