Implications for persistent chlamydial infections of phagocyte-microorganism interplay.

In vitro models of Chlamydia trachomatis inhibition by cytokines, human-monocyte derived macrophages (HMDM) and human polymorphonuclear leukocytes (HPMN) are discussed in an attempt to delineate the molecular basis of parasite-host cell interplay in persistent and chronic chlamydial infection. Interferon gamma (IFN) has been found to reversibly inhibit chlamydial growth at an early stage in the replicative cycle, while tumor necrosis factor (TNF) has a more profound effect on chlamydial growth resulting in production of aberrant reticulate bodies and enhancement of production of prostaglandin E2 (PGE2). Chlamydia trachomatis (serovar L2) replicate in HMDM while serovar K has been found to be restricted in these cells. Chlamydiae are killed by HPMN but the cell walls persist undegraded, inducing production of oxygen radicals which can be demonstrated to induce DNA strand scissions in HeLa target cells. Evidence is accumulating that chlamydia specific serum IgA antibodies may serve as a noninvasive serological marker for diagnosis of a number of acute and persistent Chlamydia trachomatis infections.

Leishmania major: inhibition of the chemiluminescent response of human polymorphonuclear leukocytes by promastigotes and their excreted factors.

The effect of various leishmanial preparations on the chemiluminescent response (CR) of human polymorphonuclear leukocytes (PMN) was studied. Almost no CR was observed with PMN stimulated with either Leishmania promastigotes or their excreted factors (EFs). Promastigotes added to PMN stimulated with phorbol myristate acetate (PMA), at a proportion of 20 to 1, respectively inhibited approximately 80-83% of the CR activity. Leishmanial promastigotes, whether live or dead, infective or non-infective as well as whole parasite homogenates, soluble and insoluble fractions, all decreased the CR of the PMN (PMN-CR). A similar effect was also observed with leishmanial EFs. The degree of inhibition was dose dependent and increasing the amount of EFs in the reaction mixture resulted in decrease of the PMN-CR. More than 80% of the total activity of the PMN-CR was inhibited by 500 micrograms EFs added at zero time to the reaction mixture. The inhibition of PMN-CR obtained from a patient suffering from a chronic infection caused by L. major was not significantly different from that observed with PMN from normal donors. The present study suggests that the PMN-CR is impaired by the Leishmania parasites and their EFs and thus may allow a greater survival of the parasites within these cells.

The persistence of Chlamydia trachomatis elementary body cell walls in human polymorphonuclear leucocytes and induction of a chemiluminescent response.

Human polymorphonuclear leucocytes (HPMN) were incubated with [35S]methionine-labelled Chlamydia trachomatis (serovar L2/434/Bu) elementary bodies (EB) and EB cell walls. No net loss in the TCA-precipitable radioactivity was observed over 24 h in the HPMN that had taken up EB cell walls. SDS-polyacrylamide gel electrophoresis of the labelled C. trachomatis EB and EB cell wall proteins extracted from the HPMN at 2 and 24 h after infection demonstrated the persistence of most of the chlamydial cell wall polypeptides. Analysis of extracts of the HPMN that had taken up either EB or EB cell walls on Urografin density gradients at 2 and 24 h after infection, and electron microscopic observations on fractions representing the peaks, demonstrated the persistence of the EB cell walls in the HPMN. Electron microscopic observations of HPMN that had taken up EB or EB cell walls demonstrated EB cell walls in the HPMN phagosomes at 24 h after infection. The HPMN exposed to EB and EB cell walls of C. trachomatis gave chemiluminescent (CL) responses with peaks respectively 12 and 7 times greater than the peak value of the control. The significance of the persistence of the EB cell wall polypeptides and cell walls in the HPMN and activation of the HPMN to produce oxygen radicals (i.e. a CL response), and its possible relation to rheumatic diseases, is discussed.

Induction of DNA strand scissions in HeLa cells by human polymorphonuclear leucocytes activated by Chlamydia trachomatis elementary bodies.

Incubation of human polymorphonuclear leucocytes (HPMN) with Chlamydia trachomatis elementary bodies (EB) or phorbol 12-myristate 13-acetate (PMA) resulted in the production of superoxide anions (.O2-) and hydrogen peroxide (H2O2). Exposure of HeLa cells to EB- or PMA-activated HPMN and to EB alone, for 2 h, resulted in the formation of DNA strand scissions (nicks) in the HeLa cells. The nicks were visualized by incorporation of biotin 11-dUTP with its detection by streptavidin-peroxidase, and quantified by using [3H]dCTP in the in situ nuclear nick-translation reaction. Catalase, and to a lesser extent superoxide dismutase, reduced the amount of nicks induced by the EB- or PMA-activated HPMN. The possible relationship between the activity of PMN in chlamydial infections and the development of chronic diseases is discussed.

Inhibitory effect of retinoic acid on the respiratory burst of adult and cord blood neutrophils and macrophages: potential implication to bronchopulmonary dysplasia.

Infants suffering from bronchopulmonary dysplasia (BPD) are known to have low levels of vitamin A, a factor which may be implicated in the pathogenesis of the condition. The ability of retinoic acid (RA) (one of the active forms of vitamin A) to influence the production of superoxide anion (02-) and hydrogen peroxide (H2O2) by stimulated human adult or cord blood neutrophils and macrophages has been studied. RA was found to inhibit the O2- and H2O2 production in a dose-dependent manner. The time required for maximal inhibition was 30 min for neutrophils and 24 h for macrophages. Although cord blood neutrophils produced larger quantities of O2- and H2O2 both with and without RA, the degree of inhibition was similar in both adult and neonatal cells (40-60%). The results suggest that retinoic acid may prevent neutrophil and macrophage mediated lung damage by inhibiting the production of toxic oxygen compounds, especially in BPD conditions.

Interaction between human polymorphonuclear leucocytes and Chlamydia trachomatis elementary bodies: electron microscopy and chemiluminescent response.

Incubation of human polymorphonuclear leucocytes (HPMN) with highly purified Chlamydia trachomatis serotype L2/434/Bu elementary bodies (EB), in the presence and absence of specific antibody, resulted in a 10(3)-fold reduction of viable count after 24 h incubation. Electron microscopy observations indicated activation of the HPMN by the EB. Attachment of the EB to the HPMN cell membrane, formation of a cytoplasmic cup and EB-containing vacuoles were observed. In addition, two types of phagocytic vacuoles were observed after 30 min incubation; in one type, a single EB was tightly surrounded by the vacuolar membrane, while the other type was enlarged and held one or more intact EB or degenerated EB or both. A fuzzy coat was observed on EB located in the HPMN vacuoles only in the presence of specific antibody. Empty vacuoles containing degenerated EB were observed in the HPMN after 24 h incubation. HPMN exposed to EB of C. trachomatis produced a marked chemiluminescent response with a peak 14 times greater than the peak value of the control. A second stimulation with phorbol 12-myristate 13-acetate and zymosan was achieved. The chemiluminescent peak value in the presence of heat-treated EB (56 degrees C, 20 min) was 50% of that obtained in the presence of untreated EB. The significance of the chemiluminescent response in the killing mechanism of C. trachomatis EB by HPMN is discussed.