IL-16 inhibits IL-5 production by antigen-stimulated T cells in atopic subjects.

BACKGROUND: We have previously shown increased expression of the CD4+ cell chemoattractant IL-16 at sites of airway allergic inflammation. Little is known about the significance of IL-16 in allergic inflammation and its role in allergen-driven T-cell cytokine responses. Because IL-16 interacts specifically with CD4+ T cells, we hypothesized that IL-16 released at sites of inflammation may modulate the pattern of cytokines produced by CD4+ T cells. OBJECTIVE: We investigated the effects of exogenous rhIL-16 on cytokine production of PBMCs from atopic and nonatopic subjects in response to antigen and PHA. METHODS: Primary cultures of freshly isolated PBMCs from ragweed-sensitive atopic subjects and nonatopic subjects were stimulated with ragweed or PHA in the presence or absence of rhIL-16. Supernatant levels of IL-4, IL-5, and IFN-gamma were determined by means of ELISA at different time points between 2 and 6 days. Effects of IL-16 on antigen-induced cellular proliferative responses were determined. RESULTS: No IL-4 protein was detected after antigen stimulation of PBMCs from atopic subjects, whereas significant levels of IL-5 were measured on day 6 (median, 534.9 pg/mL). IL-5 secretion was abolished in PBMC cultures depleted of CD4+ cells. The addition of rhIL-16 in antigen-stimulated PBMC cultures significantly reduced the amount of IL-5 released (median, 99.8 pg/mL; P <.001). Detectable levels of IFN-gamma (median, 53.3 pg/mL) were identified after antigen stimulation. The addition of rhIL-16 in antigen-stimulated PBMC cultures significantly increased IFN-gamma levels (median, 255.6 pg/mL; P <.05). Effects of rhIL-16 appear to be specific for antigen-stimulated PBMCs in atopic subjects because rhIL-16 did not alter IL-5 or IFN-gamma production in response to PHA nor did rhIL-16 alter cytokine production in nonatopic normal subjects. CONCLUSION: These studies suggest that IL-16 can play a role in regulating the production of cytokines seen in allergic states in response to antigen.

Effect of Microsphaeropsis sp. Strain P130A on Germination and Production of Sclerotia of Rhizoctonia solani and Interaction Between the Antagonist and the Pathogen.

Microsphaeropsis sp. strain P130A was evaluated for the control of tuber-borne inoculum of Rhizoctonia solani based on the viability of sclerotia produced in vitro and on both the viability and production of tuber-borne sclerotia. The interactions between the antagonist and the pathogen, as well as the effect of the toxins produced by the antagonist on mycelial growth of R. solani were studied using transmission electron microscopy. On sclerotia produced in vitro, for all incubation periods (1 to 42 days), Microsphaeropsis sp. significantly reduced germination. Percent germination of sclerotia treated with Microsphaeropsis sp. decreased with increasing incubation period from an average of 82.0% after 1 day to stabilize at an average of 5.8% after 35 days. Similarly, percent germination of tuber-borne sclerotia was significantly lower when tubers were treated with Microsphaeropsis sp. Both 2% formaldehyde and Microsphaeropsis sp. treatments significantly reduced sclerotia germination to approximately 10% after 42 days of incubation at 4 degrees C. Furthermore, on tubers treated with the antagonist, the number of sclerotia per square centimeter decreased from 1.6 to 0.5 during the 8 months of storage at 4 degrees C, whereas an increase from 1.2 to 7.8 sclerotia per square centimeter was observed on untreated tubers. Microsphaeropsis sp. (strain P130A) colonized hyphae of R. solani within 4 days after contact on culture media. Transmission electron microscopic observations showed that the antagonist induced a rupture of the pathogen plasma membrane and that a chitin-enriched matrix was deposited at sites of potential antagonist penetration. Host penetration was not associated with pathogen cell wall alterations, which occurred at the time of progress of the antagonist in the pathogen cytoplasm. In the presence of a crude extract of Microsphaeropsis sp., cells of R. solani showed cytoplasm disorganization and breakdown of plasma membranes. Antibiosis and mycoparasitism were involved in the antagonism of R. solani by Microsphaeropsis sp., but the sequence by which these events occur, as well as the significance of wall appositions produced by R. solani, is yet to be established.