Innate immunity and the normal microflora

This paper discusses the following ten subtitles with the contents indicate d. 1. To meet a microbe: discusses the four alternatives in host-microbe inter actions. 2. Receptors and signal transduction giving gene activation: discu sses the lipopolysaccharide receptor and the Limitations of cell cultures v ersus use of live animals, 3. Effector molecules - antimicrobial peptides w ith and without cysteines. A data base exists with over 500 sequences. This paper gives a general overview of five classes of gene-encoded effector mo lecules, based on the absence or presence of cysteines. These molecules are peptide antibiotics with wide spectra against different microbes. They are synthesized as propeptides and post-translational modifications are common . 4. Effectors of innate immunity - lethal action without host damage: eval uates current opinions about the mode of action of peptide antibiotics and the fact that these effectors do not create host damage. 5. Genes, introns and movable elements. Two cecropin genes containing movable elements and th e human cathelicidin gene for proFALL-39/hCAP18 are discussed. 6. The natur al microflora. Hippos or frogs as model systems. This section includes the isolation of bacteria from the normal flora of frogs; Aeromonas hydrophila, the bacterium found on all five frog species studied; arguments and select ed examples of frog-microbe interactions in vivo and in vitro; and the use of glucocorticoids as control for nuclear factor-kappa B/I kappa B alpha re gulation of effector genes. 7. The use of germ free mice - hard facts from hard work: summarizes new findings which indicate that germ-free mice are b orn with a set of antibacterial peptides in their small intestine. The inte stine of germ-free mice monoinfected with A. hydrophila have peptide patter ns that differ depending on a pretreatment with cortisone. 8. Looking back - an evolutionary perspective on innate immunity: arguments for an early ev olutionary need for gene-encoded antibacterial factors. Caenorhabditis eleg ans should provide some answers. The finding of cecropin-like peptides in H elicobacter pylori and the indications that cecropins are derived from ribo somal protein L1. 9. What about viruses? Arguments for the lack of innate i mmunity against viruses. 10. Five questions floating in the pond of immunol ogy. The normal microflora, its size and control are too often left out fro m immunological thinking. Animal model systems may sometimes invite misinte rpretation. Which animal species are more equal than others?.