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Human neutrophils require activation by mononuclear leucocyte conditioned medium to kill the pathogenic free-living
Abstract:
Naegleria fowleri is a free-living amoeba which causes a fulminant and rapidly fatal meningoencephalitis in man. Human neutrophils fail to kill the amoeba in vitro, but can do so if they are exposed to conditioned medium (CM) from PHA stimulated mononuclear leucocytes (MNLs). Specific antibody or complement was required to effect amoeba killing by CM modified neutrophils. Only short time exposure of the leucocytes to CM was required to endow them with amoebicidal properties. The CM was also shown to contain neutrophil migration inhibition activity and an activity(ies) which induced a respiratory burst in neutrophils. The results highlight the importance of MNL products other than specific antibody in neutrophil anti-microbial activity.
Insights
Human neutrophils can kill Naegleria fowleri amoebas when activated by conditioned medium from mononuclear leucocytes. This process requires specific antibody or complement, highlighting the role of leucocyte products in combating infections.
Area of Science:
- Immunology
- Infectious Diseases
- Neuroscience
Background:
- Naegleria fowleri causes fatal primary amoebic meningoencephalitis.
- Human neutrophils are crucial for innate immunity but struggle to eliminate N. fowleri in vitro.
Purpose of the Study:
- To investigate the role of mononuclear leucocytes (MNLs) and their products in enhancing neutrophil anti-amoebic activity against Naegleria fowleri.
- To identify mechanisms by which MNLs modulate neutrophil function for effective amoeba killing.
Main Methods:
- Exposure of human neutrophils to conditioned medium (CM) from PHA-stimulated MNLs.
- Assessment of amoebicidal activity of modified neutrophils against N. fowleri in vitro.
- Investigation of the requirement for specific antibody or complement in CM-mediated neutrophil activation.
- Analysis of CM for neutrophil migration inhibition and respiratory burst induction activities.
Main Results:
- Conditioned medium (CM) from stimulated MNLs enabled neutrophils to kill N. fowleri.
- Neutrophil-mediated amoeba killing required specific antibody or complement.
- Short-term exposure of MNLs to CM was sufficient to induce amoebicidal properties.
- CM contained factors inhibiting neutrophil migration and inducing respiratory burst.
Conclusions:
- Mononuclear leucocyte products, beyond specific antibodies, are critical for enhancing neutrophil anti-Naegleria fowleri activity.
- MNLs play a significant role in orchestrating the immune response against N. fowleri infections.
- Understanding these interactions could lead to novel therapeutic strategies for primary amoebic meningoencephalitis.