Influence of various factors on interferon-alpha production in cultures of human leukocytes

SARS-coronavirus replication in human peripheral monocytes/macrophages

A novel coronavirus (CoV) has been described in association with cases of severe acute respiratory syndrome (SARS). The virus, SARS-CoV, differs from the previously described human coronaviruses, 229E and OC43. 229E was previously shown to productively infect human monocytes/macrophages, whereas OC43 poorly infected the cells. In this study, we examined whether SARS-CoV could productively infect purified monocytes/macrophages (PM) derived from human donor cells. Unlike 229E-infected cells, which produced viral titers of 10^3.5 to 10⁶ TCID₅₀/ml, SARS-CoV replicated poorly in PM, producing titers of 10^1.75 to 10² TCID₅₀/ml. This finding was similar to results reported for OC43-infected cells, with titers ranging from 10^1.2 to 10^2.7 TCID₅₀/ml. Of interest, SARS-CoV proteins were detected only in PM that did not produce significant amounts of interferon (IFN)-α, and in one such case, preliminary electron microscope studies demonstrated that SARS-CoV-like particles could enter the cells, possibly via phagocytosis. These results suggest that SARS-CoV, like human CoV OC43, poorly infects human PM, and production of IFN-α by these cells further limits the infection. Given the importance of monocytes/macrophages to the immune response, it is possible that their infection by SARS-CoV and alteration of this infection by IFN-α may be important to the course of the infection in humans.

Anatomic site and immune function correlate with relative cytokine mRNA expression levels in lymphoid tissues of normal rhesus macaques

Reverse transcriptase real-time polymerase chain reaction was used to determine pro-inflammatory, anti-viral and immunoregulatory cytokine mRNA expression levels in peripheral blood mononuclear cells (PBMC) of healthy juvenile, adolescent and adult rhesus macaques. Few age-related changes in cytokine mRNA expression levels were observed. Expression of interleukin 2 and Mx, a type I interferon-inducible gene, decreased with age, whereas interleukin 4 and macrophage inflammatory protein 1 (MIP-1) alpha and beta mRNA levels increased in older monkeys. Independent of age, the pro-inflammatory cytokines [tumour necrosis factor alpha (TNF-alpha) and chemokines] were expressed at higher mRNA levels in PBMC than the immunoregulatory cytokines (interleukins 2, 4, 12). Pro-inflammatory cytokine mRNA expression levels were highest in lymphoid tissues draining mucosal surfaces. Thus, a correlation exists between cytokine mRNA levels in lymphoid tissues and the anatomical site.

Human Neutrophils Produce Macrophage Inhibitory Protein-1β but Not Type I Interferons in Response to Viral Stimulation

Several cell types have been shown to produce type I interferons (IFN). Of human leukocytes, monocytes and especially type 2 dendritic cell precursors (pDC2) seem to be the main producers and also have a wide spectrum of cytokine production. However, neutrophils seem to have a limited capacity for cytokine production but possess efficient defense mechanisms vs. bacterial infection by phagocytosis and degranulation. To determine whether they also have antiviral functions, IFN-alpha and IFN-beta were measured in preparations of pure neutrophils. The capacity of neutrophils to produce type I IFN is controversial. Additionally, macrophage inflammatory protein-1alpha (MIP-1alpha) and MIP-1beta were measured, as they are described to have indirect or direct antiviral activity. As stimulants, active and inactivated Newcastle disease virus (NDV), Sendai virus, and granulocyte colony-stimulating factor (G-CSF) were used. Peripheral blood mononuclear cells (PBMC) from the same donors were highly reactive to viral stimulation, whereas neutrophils failed to produce IFN but produced MIP-1beta in response to NDV. We conclude that neutrophils fail to prevent viral infection by IFN production but probably possess alternative mechanisms, such as secreting MIP-1beta in response to viruses.

Lowered yields of virus-induced interferon production in leukocyte cultures and risk of recurrent respiratory infections in children

OBJECTIVE

To study the correlation between the yield of virus-induced interferon (IFN) production in leukocyte cultures and the risk of recurrent respiratory infections.

METHODS

A sample of 71 consecutive children enrolled in the Finnish Otitis Media Cohort Study were selected. Children suffering from frequently recurring respiratory infections (FRRIs) were defined as the highest quintile of the entire cohort of 329 children, as regards the number of upper respiratory infections (URIs) and/or episodes of acute otitis media (AOM) during the follow-up period from 2 to 24 months.

RESULTS

In the sample of 71 children, there were 18 children with FRRI (> or = 9 URI and/or > or = 4 AOM). Leukocyte cultures, prepared from blood drawn from these 18 children at 6 months of age, produced lower yields of IFN than those of the remaining 53 children, when stimulated with adenovirus (P <0.001), coronavirus (P<0.001) or rhinovirus (P=0.002). The difference in IFN yields was even greater (P<0.001 with all three viruses) if the comparison was made between children with FRRI and those with no or maximally one URI during the follow-up period. When the IFN production capacity induced by rhinovirus was measured at the age of 24 months, a statistically significant difference between the children with FRRI and the others was also seen (P=0.002). Influenza A virus-induced IFN production capacity did not differ between the groups at either age (P=0.209).

CONCLUSIONS

Lowered IFN responses in children suffering from recurrent URIs and/or AOM may, in a subgroup of the children, be due to a genetic property of the child. However, because of the great interindividual variations, we cannot use the IFN production capacity as such for prediction of forthcoming respiratory infections and/or otitis media.

Altered cytokine production in the elderly

Elderly persons are more susceptible to bacterial and virus infections and neoplasias than young adults. This is related to an impaired immune response. Lymphocytes of the elderly show a decreased proliferation after induction with mitogens. The decreased proliferation is correlated to a decreased release of interleukin (IL)-2 and soluble IL-2 receptor (sIL-2R). However, IL-2R expression on the cell surface is normal. Interferon (IFN)-gamma as the main T-helper-1 (TH1) cytokine is produced less by lymphocytes of the elderly, whereas the TH2 cytokines IL-4 and IL-10 are produced in higher amounts as compared to stimulated lymphocytes of young donors. The decreased production of IFN-gamma is correlated to a decreased number of CD45RO+/CD8+ T cells. Therefore in the elderly there seems to be a dysregulation in the TH1/TH2-system which is predominated by TH2-functions. Monocyte function seems to be increased in the elderly. Leukocytes of elderly persons produce higher amounts of IL-1, IL-6, IL-8 and tumor necrosis factor (TNF)-alpha after induction with lipopolysaccharide (LPS) than leukocytes from young donors. In contrast, in vitro induction of IFN-alpha by viruses is decreased in the elderly compared to the young. In conclusion, there are cellular defects and dysfunctions in the elderly resulting in an altered immune response.

Determination of interferon-alpha-producing capacity in whole blood cultures from patients with various diseases and from healthy persons

To assess the clinical value of determination of the interferon (IFN)-producing capacity of patients, IFN production induced by Sendai virus (HVJ) in vitro was measured in cell cultures of whole blood from patients with various diseases. IFN production in patients with lung cancer, myelodysplastic syndromes, noninsulin-dependent diabetes mellitus, pulmonary tuberculosis, and asymptomatic HIV-1 infection was lower than that in healthy persons. Furthermore, periodic measurements of IFN production revealed decreasing IFN producing capacities in patients with lung cancer with progression of the tumor stage. However, increased IFN-producing capacities were observed in patients with tuberculosis after standard therapy. Further experiments showed that the main type of IFN induced in whole blood cultures was IFN-alpha, and decreased IFN production in patients did not result from a decreased number of leukocytes but rather from an impairment of cellular IFN production. The evaluation of IFN production in whole blood cell cultures may be a feasible method of assessing the impaired immune status.

Interleukin-1 alpha, interleukin-8 and interferon-alpha levels in gingival crevicular fluid

Cytokines play an important role in the pathology associated with chronic inflammatory diseases. We measured the total amounts [picograms (pg)] and concentrations.(pg/microliter) of interleukin-1 alpha (IL-1 alpha), interleukin-8 (IL-8) and interferon-alpha (IFN-alpha) in 20 s gingival crevicular fluid (GCF) samples obtained from 2 diseased and 2 healthy sites in 20 subjects with periodontitis, and from 2 healthy sites in 20 subjects without disease. Both the mean amount and concentration of IL-1 alpha were significantly higher (p < 0.001) in diseased sites compared to healthy sites in subjects with disease. The results for IL-8 and IFN-alpha differed depending on the method of reporting. Whereas the amount of IL-8 was significantly higher (p < 0.01) in diseased sites, the mean concentration of IL-8 was lower compared to healthy sites. The mean amount of IFN-alpha was similar in health and disease; however, the concentration of IFN-alpha was significantly lower in diseased sites (p < 0.001) corresponding to the significant increase in crevicular fluid volume (p < 0.001). There were no significant differences in the amount or concentrations of the 3 cytokines between healthy sites from subjects with disease and healthy sites from healthy controls. The total amounts of both IFN-alpha and IL-8 were correlated between healthy and diseased sites in subjects. These data suggest that, while the disease status of a site is the major determinant of the levels of these cytokines locally, subjects with high levels of IL-8 and IFN-alpha in healthy sites also tend to have high levels of these cytokines in diseased sites. Finally, both the concentrations and total amounts of IL-8 and IFN-alpha were significantly correlated in diseased sites, suggesting that levels of these two cytokines rise or fall in tandem. The combination of decreased IL-8 and decreased IFN-alpha concentrations at diseased sites may reflect the reduced anti-bacterial host defense activity at that site.

Defective production of interleukin-2 in patients with idiopathic Parkinson's disease

The pathogenesis of Parkinson's disease (PD) is largely unknown. Recently, several studies have presented evidence of an immunological dysfunction in patients suffering from PD. We studied the immune responsiveness of patients with idiopathic PD (n = 20) by investigation of the ability of peripheral blood mononuclear cells to produce cytokines after mitogenic stimulation in a whole blood assay. A group of age-related healthy blood donors served as control (n = 19). Additionally, white blood count, leukocyte differentiation and lymphocyte subtyping were performed. PD patients had a significantly higher neutrophil count, but analysis of T-cell subsets showed no difference between the two groups. In peripheral blood, secretion of interleukin-2 (IL-2) after mitogenic stimulation was significantly diminished in the patients' group (p < 0.01), whereas values of IFN-alpha 2, IL-6, IFN-gamma and sIL-2R were comparable in both groups. IL-2 production correlated negatively with the mean annual dose of levodopa treatment and correlated significantly (p < 0.002) with amantadine uptake. Analysis of sex, age, duration of illness and other drug intake revealed no correlation with cytokine release. Our findings support the view that there is a selective abnormality in the immune repertoire of peripheral blood lymphocytes in patients suffering from PD, the reasons for which need to be explored.