Cells succumbing to stress via regulated cell death (RCD) can initiate an adaptive immune response associated with immunological memory, provided they display sufficient antigenicity and adjuvanticity. Moreover, multiple intracellular and microenvironmental features determine the propensity of RCD to drive adaptive immunity. Here, we provide an updated operational definition of immunogenic cell death (ICD), discuss the key factors that dictate the ability of dying cells to drive an adaptive immune response, summarize experimental assays that are currently available for the assessment of ICD in vitro and in vivo, and formulate guidelines for their interpretation.

A series of synthetic antimicrobial peptidomimetics (SAMPs) have been prepared and found to be highly active against several Gram-negative and Gram-positive bacterial strains. These derivatives comprise the minimal structural requirements for cationic antimicrobial peptides and showed high selectivity for Gram-negative and/or Gram-positive bacteria compared to human red blood cells. We have found that SAMPs share many of the attractive properties of cationic antimicrobial peptides inasmuch that a representative SAMP was found to insert into the bilayers of large unilamellar vesicles, permeabilized both the outer and cytoplasmic membrane of Escherichia coli ML-35p, and displayed an extremely rapid bacterial killing for Staphylococcus aureus. However, while antimicrobial peptides are prone to proteolytic degradation, high in vitro stability in human blood plasma was shown for SAMPs. A combination of high antibacterial activity against methicillin-resistant staphylococci and low toxicity against human erythrocytes makes these molecules promising candidates for novel antibacterial therapeutics.

Lactoferricins are a class of antibacterial peptides isolated after gastric-pepsin digest of the mammalian iron-chelating-protein lactoferrin. For investigation of antibacterial activity, we prepared short synthetic derivatives of bovine, human, caprine, murine and porcine lactoferricins with 15-amino-acid residues of high sequence homology. The peptides corresponded to amino-acid residues 17-31 of the mature bovine lactoferrin. Only the bovine and caprine derivatives displayed measurable antibacterial activity, with the bovine one having a minimal inhibitory concentration of 24 microM and being 10 times more active than the caprine one against Escherichia coli. An alanine-scan of the bovine lactoferricin derivative was performed to identify specific amino acids that were important for the antibacterial activity. We found that neither of the two tryptophan residues (Trp 6 and Trp 8) present in the bovine lactoferricin derivative could be replaced by alanine without a major loss of antibacterial activity. The other lactoferricin derivatives tested contained only one tryptophan residue (Trp 6). Modified human, caprine and porcine lactoferricin derivatives containing two tryptophan residues (Trp 6 and Trp 8) displayed minimal inhibitory concentrations of 74, 174 and 219 microM, respectively, which represented up to a six-fold increase in antibacterial activity. The alanine-scan also revealed that the antibacterial activity was increased when acetamidomethyl-protected cysteine and unprotected glutamine (Cys 3 and Gln 7) were replaced with alanine. Only the bovine lactoferricin derivative and a few of its alanine-modified derivatives displayed measurable activity against Staphylococcus aureus.