Figure 4. Aggregation Is Linked to MBP-1 Toxicity Toward Invading Microorganisms and Host Cells In Vitro and In Vivo.

(A) TEM picture of treated E. coli. Purified MBP-1, but not the PBS control, caused local perturbations on bacterial surfaces. Rescue of the observed phenotype is obtained by co-incubating MBP-1 with OC or A11 antibodies, thereby interfering with the aggregation process.

(B) BKA with activated blood-derived eosinophils. Activated eosinophils (Eos) significantly decreased bacterial viability, whereas addition of OC reduced toxicity. Log-dilutions of bacteria were plated in triplicates. Colony-forming unit counts are reported. Values (mean levels ± % SD of one representative experiment, n = 3) are normalized to the buffer control. rIgGs, rabbit IgGs.

(C) Toxicity of MBP-118–45 to the human bronchial epithelial cell line BEAS-2B is concentration-dependent (5 hr cultures).

(D) Toxicity of MBP–118–45 (5 μM) can be inhibited by OC or heparin. Staurosporine was used as positive control. Caspase inhibition by Q-VD did not prevent cell death.

(E) Similar results were obtained with primary human bronchial epithelial cells.

(F) Immunopathology mediated by MBP-118–45 (5 μM) and its inhibition by heparin or the amyloid-binding antibody OC. The peptides were injected into the dermis of mice or applied to human skin. Skin sections were analyzed by TUNEL assay (green). Nuclei were stained with propidium iodide (red). Statistical analysis was performed (mean levels ± % SD of three independent experiments). Skin sections were also analyzed by histology (bottom). In mice, MBP-118–45 reduced the numbers of keratinocytes. In human skin, application of the toxin resulted in pyknotic, shrunken, and irregularly shaped keratinocytes. AU, arbitrary unit.