Neutrophils Are More Effective than Monocytes at Phagosomal Containment and Killing of Listeria monocytogenes

Neutrophils and inflammatory monocytes are innate immune cells essential for protection during Listeria monocytogenes infection. Although certain functions have been generally assigned to each of the cells, similarities and differences in functions necessary for bacterial clearance have not previously been investigated. In the current study, phagocytosis, phagosomal containment, bacterial killing, and cytokine production by neutrophils and monocytes during L. monocytogenes infection were studied. Data obtained via in vitro studies show that neutrophils are more effective at L. monocytogenes uptake, phagosomal containment, and killing than monocytes. However, monocytes were found to be more effective at cytokine production during L. monocytogenes infection, in vivo. Additionally, the data demonstrated that neutrophils and monocytes are also capable of producing IL-1α, a cytokine that does not yet have a clearly defined role during infection with L. monocytogenes. Furthermore, we were able to demonstrate a population of monocytes producing both TNF-α and IL-α, concurrently. This study highlights the multifunctional capabilities of neutrophils and monocytes, further adding to our knowledge of these innate immune cells during L. monocytogenes infection.