Multidimensional Immunomodulation

Antimicrobial function of the GAPDH-related antimicrobial peptide in the skin of skipjack tuna, Katsuwonus pelamis

A 3.4 kDa of antimicrobial peptide was purified from an acidified skin extract of skipjack tuna, Katsuwonus pelamis, by preparative acid-urea-polyacrylamide gel electrophoresis and C18 reversed-phase HPLC. A comparison of the N-terminal amino acid sequence of the purified peptide with that of other known polypeptides revealed high sequence homology with the YFGAP (Yellowfin tuna Glyceraldehyde-3-phosphate dehydrogenase-related Antimicrobial Peptide); thus, this peptide was identified as the skipjack tuna GAPDH-related antimicrobial peptide (SJGAP). SJGAP showed potent antimicrobial activity against Gram-positive bacteria, such as Bacillus subtilis, Micrococcus luteus, Staphylococcus aureus, and Streptococcus iniae (minimal effective concentrations [MECs], 1.2-17.0 μg/mL), Gram-negative bacteria, such as Aeromonas hydrophila, Escherichia coli D31, and Vibrio parahaemolyticus (MECs, 3.1-12.0 μg/mL), and against Candida albicans (MEC, 16.0 μg/mL) without significant hemolytic activity. Antimicrobial activity of this peptide is heat-stable but salt-sensitive. According to the secondary structural prediction and the homology modeling, this peptide consists of three secondary structural motifs, including one α-helix and two parallel β-strands, and forms an amphipathic structure. This peptide showed neither membrane permeabilization ability nor killing ability, but did display a small degree of leakage ability. These results suggest that SJGAP acts through a bacteriostatic process rather than bactericidal one. SJGAP is another GAPDH-related antimicrobial peptide isolated from skipjack tuna and likely plays an important role for GAPDH in the innate immune defense of tuna fish.

Purification and characterization of YFGAP, a GAPDH-related novel antimicrobial peptide, from the skin of yellowfin tuna, Thunnus albacares

A 3.4 kDa of antimicrobial peptide was purified from an acidified skin extract of the yellowfin tuna, Thunnus albacares, by preparative acid-urea-polyacrylamide gel electrophoresis and C(18) reversed-phase HPLC. A comparison of the N-terminal amino acid sequence of the purified peptide with that of other known polypeptides revealed high homology with the N-terminus of glyceraldehyde-3-phosphate dehydrogenase (GAPDH); thus, this peptide was designated as the yellowfin tuna GAPDH-related antimicrobial peptide (YFGAP). YFGAP showed potent antimicrobial activity against Gram-positive bacteria, such as Bacillus subtilis, Micrococcus luteus, and Streptococcus iniae (minimal effective concentrations [MECs], 1.2-17.0 μg/mL), and Gram-negative bacteria, such as Aeromonas hydrophila, Escherichia coli D31, and Vibrio parahaemolyticus (MECs, 3.1-12.0 μg/mL) without significant hemolytic activity. According to the secondary structural prediction and the homology modeling, this peptide forms an amphipathic structure and consists of three secondary structural motifs including one α-helix and two parallel β-strands. This peptide did not show membrane permeabilization ability and its activity was bacteriostatic rather than bactericidal. This is the first report of the isolation of an antimicrobial peptide from a tuna species and the first description of the antimicrobial function of the N-terminus of GAPDH of an animal species.

Fundamentals of clinical immunotoxicology

Whereas animal studies are invaluable for screening various chemical and drugs for immunotoxic potential, such systems are necessarily limited in their predictive value for humans given the differences in physiology, immune system structure and function, and various other parameters between humans and nonhuman animals. However, prospective experimental studies in humans are not always practical or ethical. What is needed is an approach for combining animal data, human data collected in the course of clinical studies, and modern tools of bioinformatics and systems biology. In this chapter, we will explore current assays and methodologies for assessing immunotoxic potential in humans using this multi--parameter approach.

Respiratory immunotoxicity: An in vitro assessment

As yet, in vitro assessment of the immunotoxic potency of respiratory agents is not possible. The complexity of the endpoint and the respiratory tract, and the limited availability of well-documented respiratory agents are the main reasons. The evidence that epithelial cells (ECs) are triggered by compounds to express in vitro surface proteins and soluble mediators, has stimulated their use for developing tests for respiratory immunotoxicity. A variety of airway ECs and EC-lines have been assessed, but the available information seems to point at human alveolar cells (e.g., A549) as the most convenient cell type. EC-based test formats with various degrees of complexity have been assessed. Sofar, promising results were obtained using a 3D model using the human A549 lung cell line. Dendritic cells (DCs) have been subjected to intensive research. However, currently available tests are not well suited to discern among the potency of sensitizers. Potential explanations include the lack of standardised protocols for the generation of DCs, no good standards for estimating the quality of in vitro derived DC-cultures, and limited dynamics of the currently used end-points. Alveolar macrophages (AMs) have so far received less attention. This may proof unjustified as macrophages may link innate responses to adaptive immunity. The observation that ECs, DCs and AMs affect each other, suggests that test formats are required combining at least two of these cell types if ranking of compounds according to their sensitising potency is the aim. In addition, the capacity of compounds to cross a cellular membrane is an important property of an immunotoxic compound, which can be assessed only in 3D reconstituted human tissue models. While promising data have been reported for the skin, immunocompetent 3D reconstituted human lung remains to be evaluated for respiratory immunotoxicity. Obviously, the success of any of these simplified test (as compared to the complexity of the immune response) is highly dependent on the availability of early stage biomarkers (expressed at mucosal barrier level) that are predictive for relevant immunotoxicity mechanisms occurring down-stream of the immune response. As yet, such biomarkers are not yet available.