SUMMARYAcute RSV infection in infancy may produce some asthma-like symptoms and may be followed by a recurrent wheeze later in childhood. It has been proposed that RSV infection stimulates type-2 cytokine responses, resembling those found in atopy and asthma. Peripheral blood cells were obtained from RSVinfected infants (n 30) and healthy controls (n 10). After in vitro restimulation of the cells, intracellular IL-4 and interferon-gamma (IFN-g) were measured by flow cytometry. The cells from RSV-infected infants produced more IL-4 and less IFN-g than those from healthy controls. IL-4 production was more frequent in CD8 than in CD4 cells, and the bias toward IL-4 production was greatest in infants with mild infections, whereas IFN-g production increased with disease severity. Our conclusions are that RSV infection is associated with IL-4 production in peripheral T cells, and that peripheral blood in infants with severe disease may be depleted of cytokine-producing cells.

In this study, two different hantaviruses, Puumala virus (PUUV) and Dobrava virus (DOBV), were demonstrated for the first time to coexist and cause hemorrhagic fever with renal syndrome (HFRS) in Croatia. Phylogenetic analysis showed some differences among the nucleotide sequences of PUUV originating from Dinara mountain, which was more closely related to Austrian PUUV than other Croatian PUUV from Mala Kapela mountain. More consistency was found among the Croatian DOBV. HFRS was verified in 85 of 201 suspected cases recorded in 1995 during the largest HFRS outbreak in Croatia. Most of these cases were soldiers. With the exception of the coastal region and islands, all of Croatia was found to be an area endemic for HFRS. A statistically significantly higher proportion of DOBV-infected patients had acute renal failure, visual disturbance, severe thrombocytopenia, and elevated levels of nonsegmented leukocytes, creatine, and total bilirubin. The prevalence of gastrointestinal and electrocardiography disorders also was greater in DOBV-infected patients. Interestingly, significantly more PUUV-infected patients had elevated systolic blood pressure on admission to the hospital. Further prospective studies are necessary to shed more light on differences in HFRS severity associated with PUU and DOB viruses.

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SUMMARYThe fusion protein of the respiratory syncytial virus (RSV) binds to the pattern recognition receptors, TLR4 and CD14, and initiates innate immunity response to the virus. The aim of the study was to investigate the expression of TLR4 on peripheral blood lymphocytes and monocytes in peripheral blood of infants in both acute and convalescent phase of RSV bronchiolitis ( n = 26). In addition, TNF-a expression in lipopolysaccharide-stimulated monocytes was also assessed. The results showed TLR4 to be expressed predominantly by monocytes in both sick infants and controls. During the acute phase of infection monocytes up-regulated TLR4 in eight infants, which returned to the levels recorded in controls 4-6 weeks from infection. There was no difference in the percentage of TNF-a secreting monocytes. Of the clinical parameters tested, minimal oxygen saturation was found to correlate negatively with this expression in the group of infants with increased TLR4. Additional studies are under way to correlate this finding with the outcome of the immune response to RSV.

This study asks how T helper (TH) subset cytokines impact upon IL‐12‐directed change in B cells engaged in signaling via the B cell receptor and CD40, essential components in the initiation of T‐dependent B cell responses. For B cells stimulated in this way, IL‐12 promoted a distinct phenotype highlighted by the hyper‐expression of CD38: the Th1 cytokine IFN‐γ reproduced the IL‐12 effects while neutralizing antibody to IFN‐γ reversed IL‐12‐dependent change. The divergent pathway of differentiation promoted by the Th2 cytokine IL‐4 (characterized by hyper‐induction of CD23) was left unchecked by IL‐12. IL‐10 was found to dampen IL‐12 actions by suppressing IL‐12‐dependent IFN‐γ production but failed to perturb the effects of exogenous IFN‐γ. Thus, IL‐12 – by invoking autocrine IFN‐γ production – promotes phenotypic deviation in B cells engaging T‐dependent signals. The reversal of such Th1 driving of B cells by IL‐10 only when the source of IFN‐γ is endogenous and the inability of IL‐12 to impact upon IL‐4‐directed differentiation suggest a progressive and hierarchical commitment of B cells to polarization during a developing T‐dependent response dominated at the level of the Th cell rather than that of the dendritic cell.

SUMMARYWhether CD5 on B cells marks a subset functionally distinct from the conventional CD5 negative (CD5 neg ) adult population or is more an indicator of activation, remains contentious. Here we have investigated whether CD5 positive (CD5 pos ) and CD5 neg B cells can be distinguished in terms of their response to surrogate signals aimed to model, in vitro, T-cell dependent (TD) and Tindependent (TI) encounters with antigen in vivo: the predominantly CD5 pos B-cell population found in cord blood, CD5 B cells positively selected from tonsils and their CD5 neg counterparts, were compared. Neonatal B cells displayed a near-identical phenotype to that of adult CD5 pos B cells, being characterized by uniform immunoglobulin M (IgM), immunoglobulin D (IgD), CD23 and CD44 coexpression. When cultured with anti-IgM maintained at high density on CD32-tranfected mouse L cells to model TI responses or on CD40 ligand (CD40L)-bearing L cells (with or without captured anti-IgM) to model TD encounters, DNA synthesis was stimulated to a similar extent in all three populations. Focusing on CD5 and CD23, we found that ± although the signals delivered promoted distinct pro®les of expression ± under each condition of activation, the phenotypes that emerged for adult CD5 pos and CD5 neg B cells were remarkably similar. Neonatal B cells displayed a greater diminution in CD5 expression than adult CD5 pos B cells following CD40 signals but otherwise the two populations again behaved similarly. The inclusion of interleukin-4 (IL-4) to cultures where cells were costimulated via surface (s)IgM and CD40 resulted in a complete loss of CD5 expression and a corresponding hyperexpression of CD23, irrespective of the population studied. The near-identical response of CD5 pos and CD5 neg B cells to surrogate TD or TI signals in vitro and their convergence to indistinguishable phenotypes is wholly supportive of CD5 being a¯uctuating marker of activation rather than it delineating functionally distinct subsets.

BackgroundToll-like receptors (TLRs) are part of the innate immune system, able to recognize pathogen-associated molecular patterns and activate immune system upon pathogen challenge. Respiratory syncytial virus (RSV) is a RNA virus particularly detrimental in infancy. It could cause severe lower respiratory tract disease and recurrent infections related to inadequate development of anti-viral immunity. The reason could be inadequate multiple TLRs engagement, including TLR8 in recognition of single-stranded viral RNA and diminished synthesis of inflammatory mediators due to a lower expression.MethodsIntracellular TLR8 expression in peripheral blood monocytes from RSV-infected infants was profiled and compared to healthy adults and age matched controls. Whether the observed difference in TLR8 expression is a transitory effect, infants in convalescent phase (4-6 weeks later) were retested. Specific TLR8-mediated TNF-α production in monocytes during an acute and convalescent phase was analyzed.ResultsRSV-infected and healthy infants had lower percentage of TLR8-expressing monocytes than healthy adults whereas decreased of TLR8 protein levels were detected only for RSV-infected infant group. Lower protein levels of TLR8 in monocytes from RSV-infected infants, compared to healthy infants, negatively correlated with respiratory frequency and resulted in lower TNF-α synthesis upon a specific TLR8 stimulation. In the convalescent phase, levels of TLR8 increased, accompanied by increased TNF-α synthesis compared to acute infection.ConclusionsLower TLR8 expression observed in monocytes, during an acute RSV infection, might have a dampening impact on early anti-viral cytokine production necessary to control RSV replication, and subsequently initiate an adaptive Th1 type immune response leading to severe disease in infected infants.

Infection with respiratory syncytial virus (RSV) may induce asthma-like symptoms and RSV-specific IgE in infected infants as a result of Th2-like response to RSV. The effect of RSV infection on the expression of B cell antigens CD21 and CD23, putative participants in Th2 responses, was investigated. Samples from bronchiolitic infants (n = 19) were tested by three-color immunofluorescence flow cytometry during the acute phase of infection and 4-6 weeks later. In 6 of 10 RSV-positive infants, the percentage of CD23+ B cells was higher than in 9 RSV-negative children and in controls. Both CD21+ and CD21- B cells exhibited a higher percentage of CD23. The group with increased expression of CD23 antigen had RSV-specific IgE and IgG4 antibodies. These findings corroborate the hypothesis that RSV could provoke a Th2-type response, but the relationship between CD23 antigen and RSV infection must be determined.