Introduction: The Porcine Myeloid Antibacterial Peptide (PMAP)-23 is a porcine host
defence peptide with strong antibacterial activity against Gram-positive and Gram-negative bacteria,
Objective: PMAP-23 and truncated/mutated derivatives were tested for antibacterial and immunomodulatory
activities to determine core elements of the peptide required for functionality.
Methods: PMAP-23 and truncated and/or mutated derivatives were synthesized. Antibacterial activity
against Gram positive and negative bacteria was determined using colony counting assays.
Cytotoxicity was measured against red blood cells and epithelial cells. Peptide induced cytokine
production of epithelial cells was determined by ELISA. LPS neutralization was measured using
isothermal titration calorimetry and inhibition of LPS induced cytokine production by macrophages.
The effect of peptides on phagocytosis was performed by measuring uptake of fluorescently
labelled beads by porcine macrophages.
Results: Truncation of the peptide did not lead to a strong reduction in antibacterial activity, but
interestingly, all C-terminal truncated forms were strongly inhibited by salt addition, unlike the full
length peptide or the two N-terminally truncated peptides. None of the peptides were hemolytic or
toxic in concentrations up to 40 μM. Full length PMAP-23 induced IL-8 production in porcine
epithelial cells, however, this activity was lost in all truncated peptides. None of the peptides bound
LPS and subsequently did not inhibit LPS-induced cytokine production of monocytes. Finally, all
PMAP-23 derived peptides reduced the uptake of beads by freshly isolated monocytes.
Conclusion: PMAP-23 is mainly antibacterial with only limited immunomodulating capacity; the
full length peptide is required for the full spectrum of activities.