Activated human eosinophils synthesize new proteins

Human eosinophils stimulate DNA synthesis and matrix production in dermal fibroblasts

Fibrosis is frequently found in diseases exhibiting tissue eosinophilia, such as some parasitic worm infections, eosinophilia-myalgia syndrome, and eosinophilic fasciitis. Previously, eosinophil extracts have been shown to induce proliferation in neonatal foreskin fibroblasts in vitro. To determine if living eosinophils can induce synthesis of DNA and components of the extracellular matrix in dermal fibroblasts, we cultured purified human eosinophils for 2 or 7 days in the presence of the eosinophil-active cytokines granulocyte/macrophage colony stimulating factor, interleukin-3, or interleukin-5, and added eosinophil-conditioned medium to cultures of dermal fibroblasts. Using flow cytometry, we found that eosinophil-conditioned medium increased by two-fold the percentage of fibroblasts in S-phase. This stimulation of fibroblast DNA synthesis was corroborated using a standard tritiated thymidine assay and the two methods were shown to correlate well with each other. Eosinophil-conditioned medium stimulation of DNA synthesis was dose dependent and conditioned medium from eosinophils treated with any one of the three cytokines induced increased DNA synthesis. Treatment of fibroblasts with cytokines alone did not induce enhanced DNA synthesis. Eosinophil-conditioned medium also affected fibroblast matrix production. Eosinophil-conditioned medium induced a two-fold increase in soluble and cell-associated fibroblast glycosaminoglycan production and a 76% increase in collagen production. These observations support the concept that eosinophils may be active contributors to the pathophysiology of eosinophil-associated fibrotic disease.

The destruction of virulent Entamoeba histolytica by activated human eosinophils

Unlike normal (i.e., non-activated) human eosinophils that are unable to destroy virulent Entamoeba histolytica even in the presence of antibodies and complement, activated eosinophils effectively destroy the parasite in vitro without the help of opsonins, yet increase this capacity with their assistance. Many activated eosinophils succumb in the process as well, probably victims of toxic products released by dying amoebae. Human activated eosinophils thus behave more like activated macrophages than like neutrophil polymorphonuclear leucocytes that are notoriously incompetent in dealing with virulent amoebae. As a regular constituent of early inflammatory reactions, and notwithstanding the absence of blood and tissue eosinophilia in invasive amoebiasis, the activated eosinophil may play a role in the defence against E. histolytica.

Release of granule proteins by eosinophils from allergic and nonallergic patients with eosinophilia on immunoglobulin-dependent activation

The release of eosinophil peroxidase (EPO) and eosinophil cationic protein (ECP) was evaluated after incubation of eosinophils (EOSs) from allergic subjects with the specific allergen or with anti-IgE monoclonal antibodies (MAbs). High levels of EPO could be released after addition of the specific allergen (and not unrelated ones) or anti-IgE MAb. Moreover, EPO release with the two stimuli was significantly correlated both in allergic and in nonallergic patients. In the same supernatants, another granule protein, ECP, could not be detected, suggesting a lack of correlation between EPO and ECP release after IgE-dependent stimulation. However, when EOSs with surface-IgA antibodies were incubated with anti-IgA MAb, both EPO and ECP were released. In contrast, incubation of EOSs with anti-IgG MAb induced mainly the release of ECP and not EPO. These results indicate that pharmacologically active mediators can be released by EOSs from allergic and nonallergic patients on immunoglobulin-dependent activation. The results also confirm the hypothesis of a selective release of the various granule proteins and raise the question of transduction signals delivered by the three Fc receptors (Fc epsilon R, FC alpha R, and FC gamma R) present on human EOSs.

Phosphorylation and dephosphorylation of soluble proteins in human eosinophils

The effect of phorbol 12-myristate 13-acetate (PMA), calcium ionophore (A23187), opsonized zymosan (OZ), and N-formylmethionyl-leucyl-phenylalanine (f-Met-Leu-Phe) on protein phosphorylation was examined in purified eosinophils (eos) isolated from human peripheral blood. Eos were prelabeled with [32P]orthophosphate, stimulated with several activating agents for varying periods of time. The soluble proteins were then analyzed by one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography. In resting eos, there was phosphorylation of endogenous soluble proteins with molecular weights of 12, 16, 21, 40, and 66 kilodaltons (kDa). PMA, a potent activator of oxidative metabolism, induced phosphorylation of 19-, 40-, and 67-kDa proteins. A23187, a strong degranulating stimulus, caused phosphorylation of 40-, 53-, and 67-kDa proteins. OZ, a relatively weak stimulus for eos function, caused phosphorylation of 30-34-, 59-, 67-, and 93-kDa proteins. In addition, all the above stimuli caused a time-dependent dephosphorylation of 21-kDa protein. In contrast, f-Met-Leu-Phe caused neither phosphorylation of new proteins nor dephosphorylation of preexisting eos proteins. These findings demonstrate that selected stimuli affect phosphorylation of soluble eos protein. These results also suggest that phosphorylation of specific proteins in eos is an intermediary step in external stimulus-induced cell activation, which may involve many different cell functions.