Background:
Macrophages, an important component of immunity, are divided into subpopulations based on their functional phenotypes.
Aims:
1. Establish a predominant M1 and M2 polarisation pattern in vitro.

2. Examine the inflammatory cytokine response to bacterial stimulation in polarised cells.

3. Determine the phagocytic activity in polarised cells after stimulation with bacteria.

Material and Methods:
Peritoneal and bone marrow derived macrophages were harvested from C57BL/6 mice. Cells were exposed to polarising stimuli for 18-24 hours. LPS and IFN-γ were used to induce M1 and IL-4 was used to induce M2. ELISA was performed on the supernatant to confirm the M1 and M2 phenotypes. Polarised cells were further stimulated with heat-killed S. aureus and S. Typhi or FITC-labeled E coli. Inflammatory cytokine production and phagocytosis were assessed by ELISA and FACScan analysis.

Result:
M1 macrophages were characterised by high levels of TNF-alpha and IL-12p70. M2 macrophages were characterised by high levels of TGF-beta and low levels of IL12p70. M1 polarized macrophages, when exposed to gram-positive and gram-negative bacteria, had lower levels of TNF-alpha than M2 macrophages. Phagocytosis assays revealed similar results for both M1 and M2 macrophages.

Conclusion:
M1 macrophages are expected to produce higher levels of TNF-alpha, however we found that M1 macrophages exposed to bacterial stimulation had lower levels of TNF-alpha compared with their M2 counterparts. This unexpected result indicates a tolerisation effect developed during the M1 polarisation, and further work is required to clarify the underlying mechanism(s).