Low number of antibody producing cells in patients with sickle cell anemia

Inflammatory status in pediatric sickle cell disease: Unravelling the role of immune cell subsets

Introduction: The mutation of the beta-globin gene that causes sickle cell disease (SCD) results in pleiotropic effects, such as hemolysis and vaso-occlusive crisis that can induce inflammatory mechanisms with deleterious consequences on the organism. Moreover, SCD patients display an increased susceptibility to infections. Few studies are currently available that evaluate a wide immunological profile in a pediatric population. This study proposes an evaluation of the immune profile in subjects with SCD in a pediatric population through a detailed analysis by flow cytometry. Methods and Materials: Peripheral blood samples from 53 pediatric patients with SCD (mean age 9.8 years, interquartile range 9 years) were obtained and then analyzed by flow cytometry, in order to evaluate changes in the immune populations compared to 40 healthy donors (mean age 7.3 years, interquartile range 9.5 years). Results: Our data showed an increase in neutrophils (with a reduction in the CD62L + subpopulation) and monocytes (with a decrease in HLA-DRlow monocytes) with normal values of lymphocytes in SCD patients. In the lymphocyte subpopulations analysis we observed lower values of CD4⁺ T cells (with higher number of memory and central memory T lymphocytes) with increased frequency of CD8⁺ T cells (with a predominant naive pattern). Moreover, we observed higher values of CD39⁺ Tregs and lower HLA-DR+ and CD39^- T cells with an increased Th17, Th1-17 and Th2 response. Conclusion: We observed immunological alterations typical of an inflammatory status (increase in activated neutrophils and monocytes) associated with a peculiar Treg pattern (probably linked to a body attempt to minimize inflammation intrinsic to SCD). Furthermore, we highlighted a T helper pathway associated with inflammation in line with other studies. Our data showed that immunological markers may have an important role in the understanding the pathophysiology of SCD and in optimizing targeted therapeutic strategies for each patient.

In-Depth Immunological Typization of Children with Sickle Cell Disease: A Preliminary Insight into Its Plausible Correlation with Clinical Course and Hydroxyurea Therapy

Sickle cell disease (SCD) is a condition of functional hypo-/a-splenism in which predisposition to bacterial infections is only a facet of a wide spectrum of immune-dysregulation disorders forming the clinical expression of a peculiar immunophenotype. The objective of this study was to perform an in-depth immunophenotypical characterization of SCD pediatric patients, looking for plausible correlations between immunological biomarkers, the impact of hydroxyurea (HU) treatment and clinical course. This was an observational case−control study including 43 patients. The cohort was divided into two main groups, SCD subjects (19/43) and controls (24/43), differing in the presence/absence of an SCD diagnosis. The SCD group was split up into HU+ (12/19) and HU− (7/19) subgroups, respectively receiving or not a concomitant HU treatment. The principal outcomes measured were differences in the immunophenotyping between SCD patients and controls through chi-squared tests, t-tests, and Pearson’s correlation analysis between clinical and immunological parameters. Leukocyte and neutrophil increase, T-cell depletion with prevalence of memory T-cell compartment, NK and B-naïve subset elevation with memory and CD21low B subset reduction, and IgG expansion, significantly distinguished the SCD HU− subgroup from controls, with naïve T cells, switched-memory B cells and IgG maintaining differences between the SCD HU+ group and controls (p-value of <0.05). The mean CD4+ central-memory T-cell% count was the single independent variable showing a positive correlation with vaso-occlusive crisis score in the SCD group (Pearson’s R = 0.039). We report preliminary data assessing plausible clinical implications of baseline and HU-related SCD immunophenotypical alterations, which need to be validated in larger samples, but potentially affecting hypo-/a-splenism immuno-chemoprophylactic recommendations.

Allogeneic haematopoietic stem cell transplantation resets T- and B-cell compartments in sickle cell disease patients

Objectives

Allogeneic haematopoietic stem cell transplantation (allo-HSCT) is the only currently available curative treatment for sickle cell disease (SCD). Here, we comprehensively evaluated the reconstitution of T- and B-cell compartments in 29 SCD patients treated with allo-HSCT and how it correlated with the development of acute graft-versus-host disease (aGvHD).

Methods

T-cell neogenesis was assessed by quantification of signal-joint and β-chain TCR excision circles. B-cell neogenesis was evaluated by quantification of signal-joint and coding-joint K-chain recombination excision circles. T- and B-cell peripheral subset numbers were assessed by flow cytometry.

Results

Before allo-HSCT (baseline), T-cell neogenesis was normal in SCD patients compared with age-, gender- and ethnicity-matched healthy controls. Following allo-HSCT, T-cell neogenesis declined but was fully restored to healthy control levels at one year post-transplantation. Peripheral T-cell subset counts were fully restored only at 24 months post-transplantation. Occurrence of acute graft-versus-host disease (aGvHD) transiently affected T- and B-cell neogenesis and overall reconstitution of T- and B-cell peripheral subsets. B-cell neogenesis was significantly higher in SCD patients at baseline than in healthy controls, remaining high throughout the follow-up after allo-HSCT. Notably, after transplantation SCD patients showed increased frequencies of IL-10-producing B-regulatory cells and IgM⁺ memory B-cell subsets compared with baseline levels and with healthy controls.

Conclusion

Our findings revealed that the T- and B-cell compartments were normally reconstituted in SCD patients after allo-HSCT. In addition, the increase of IL-10-producing B-regulatory cells may contribute to improve immune regulation and homeostasis after transplantation.

Inflammatory Dendritic Cells Contribute to Regulate the Immune Response in Sickle Cell Disease

Sickle cell disease (SCD), one of the most common hemoglobinopathies worldwide, is characterized by a chronic inflammatory component, with systemic release of inflammatory cytokines, due to hemolysis and vaso-occlusive processes. Patients with SCD demonstrate dysfunctional T and B lymphocyte responses, and they are more susceptible to infection. Although dendritic cells (DCs) are the main component responsible for activating and polarizing lymphocytic function, and are able to produce pro-inflammatory cytokines found in the serum of patients with SCD, minimal studies have thus far been devoted to these cells. In the present study, we identified the subpopulations of circulating DCs in patients with SCD, and found that the bloodstream of the patients showed higher numbers and percentages of DCs than that of healthy individuals. Among all the main DCs subsets, inflammatory DCs (CD14⁺ DCs) were responsible for this rise and correlated with higher reticulocyte count. The patients had more activated monocyte-derived DCs (mo-DCs), which produced MCP-1, IL-6, and IL-8 in culture. We found that a CD14⁺ mo-DC subset present in culture from some of the patients was the more activated subset and was mainly responsible for cytokine production, and this subset was also responsible for IL-17 production in co-culture with T lymphocytes. Finally, we suggest an involvement of heme oxygenase in the upregulation of CD14 in mo-DCs from the patients, indicating a potential mechanism for inducing inflammatory DC differentiation from circulating monocytes in the patients, which correlated with inflammatory cytokine production, T lymphocyte response skewing, and reticulocyte count.

Immune mechanisms involved in sickle cell disease pathogenesis: current knowledge and perspectives

Sickle cell disease (SCD) is caused by a single point mutation in the β-chain of the hemoglobin gene that results in the replacement of glutamic acid with valine in the hemoglobin protein. However, recent studies have demonstrated that alterations in several other genes, especially immune related genes, may be associated with complications of SCD. In fact, higher chronic inflammatory status is related to more severe clinical symptoms in SCD patients, suggesting crucial roles of the immune system in SCD physiopathology. Nevertheless, although participation of innate immune cells in SCD pathogenesis has been broadly and extensively described, little is known about the roles of the adaptive immune system in this disease. In addition, the influence of treatments on the immune system of SCD patients and their complications (such as alloimmunization) are not yet completely understood. Thus, we reviewed the current knowledge about the immune mechanisms involved in SCD pathogenesis. We suggest recommendations for future studies to allow for a broader understanding of SCD pathogenesis, helping in the development of new therapies and improvement in the life quality and expectancy of patients.

Sickle Cell Anemia Patients Display an Intricate Cellular and Serum Biomarker Network Highlighted by TCD4+CD69+ Lymphocytes, IL-17/MIP-1β, IL-12/VEGF, and IL-10/IP-10 Axis

BACKGROUND

Sickle cell anemia (SCA) is associated with a chronic proinflammatory state characterized by elevated leukocyte count, mortality from severe recurrent infections, and subsequent vasoocclusive complications with leukocyte adhesion to the endothelium and increased plasma levels of inflammatory cytokines. The immune system has a close connection with morbidity in SCA, but further studies are needed to uncover the involvement of innate and adaptive immunities in modulating the SCA physiopathology. We performed measurements of the frequency of innate and adaptive immunity cells, cytokines, chemokines, and growth factors and immunophenotyping of Toll-like receptor and adhesion molecule expression in the blood of SCA patients and healthy donors to evaluate the different profiles of these biomarkers, the relationship among them, and their correlation to laboratory records and death risk. Material and Methods. Immunophenotyping of cells, Toll-like receptors, and adhesion molecules were performed from peripheral blood samples of SCA patients and healthy donors by flow cytometry and cytokine/chemokine/growth factor measurement by the Luminex technique performed from the serum of the same subjects.

RESULTS

Cells of adaptive immunity such as IL-12, IL-17, and IL-10 cytokines; IL-8, IP-10, MIP-1α, MIP-1β, and RANTES chemokines; and VEGF, FGF-basic, and GM-CSF growth factors were higher in SCA patients than healthy donors regardless of any laboratorial and clinical condition. However, high death risk appears to have relevant biomarkers.

CONCLUSION

In the SCA pathophysiology at steady state, there is a broad immunological biomarker crosstalk highlighted by TCD4+CD69+ lymphocytes, IL-12 and IL-17 inflammatory and IL-10 regulatory cytokines, MIP-1α, MIP-1β, and IP-10 chemokines, and VEGF growth factor. High expression of TLR2 in monocytes and VLA-4 in TCD8+ lymphocytes and high levels of MIP-1β and RANTES appear to be relevant in high death risk conditions. The high reticulocytosis and high death risk conditions present common correlations, and there seems to be a balance by the Th2 profile.

Genetic diversity of CD14, CD28, CTLA-4 and ICOS gene promoter polymorphism in African and American sickle cell disease

Variable immune response to external stimuli remains a major concern in sickle cell disease (SCD), with such responses predicted to be contributors to disease pathogenesis. Elucidating the diversity of host genes contributing to immune response would assist to clarify differing outcomes among and between disease groups. We hypothesize that there is a significant interethnic diversity in the CD14 (rs2569190), CD28 (rs35593994), CTLA-4 (rs5742909) and ICOS (rs4404254) gene polymorphisms among and between SCD groups. We genotyped single nucleotide polymorphisms of the 4 loci among African and African American SCD and control groups and between SCD groups. In all, 375 individuals from Mali (145 SCD and 230 controls) and 700 DNA samples from the United States (321 SCD and 379 controls) were subjected to a PCR-RFLP assay. We found no intraethnic difference in genotypic and allelic frequencies of the 4 loci among Africans and African Americans, potentially significant in disease association studies, including a similar observation for interethnic frequencies of CD28, CTLA-4 and ICOS genes, but not CD14. The CD14 (rs2569190) gene promoter demonstrated a significant difference (p < 0.02) between African and African American SCD groups, with the mutant variant (-159 T/T) more frequent (p < 0.0002) in African American SCD (38.9% versus 26.2%). The higher frequency of CD14 mutants among African Americans without an accompanying defect in CD28, CTLA-4 and ICOS diversity possibly indicates a defective innate response, driven by CD14, is untethered to downstream T cell differentiation or effector function. Additionally, we show that CD28 (rs35593994) mutant variants have no impact on T cell differentiation, as the ICOS gene provides an alternative pathway to override this impairment. We conclude that in spite of the defect in CD14, T cell selection and differentiation is unimpeded and a robust adaptive immune response initiated.

Tuberculosis in children with sickle cell anaemia: a retrospective study in French tertiary care centres

Tuberculosis (TB) and sickle cell anaemia (SCA) may affect the same population of patients, particularly in Africa but also in high-TB incidence areas in developed countries. However, few data are available from children with SCA who develop TB. The aim of this study was to describe the clinical features and outcome of TB diagnosed in children with SCA. We conducted a retrospective, descriptive study in three referral centre of Sickle Cell Disease in Paris, France. We included 11 patients with SCA who develop TB. The median age at TB diagnosis was 11 years [7.5-14.5]. Two patients were asymptomatic and nine patients were symptomatic. Six patients had pulmonary TB (pulmonary, pleural and mediastinal lesions). Five patients had extrapulmonary TB (osteoarticular TB, hepatic TB, cervical and mediastinal TB). Mycobacterium tuberculosis was isolated in four of the 11 cases. All patients recovered after a median of 6 months of anti-TB treatment. The localisation of TB and outcome after treatment in our SCA patients were similar to the one observed in an age-and sex-matched control group of non-SCA patient with TB.

CONCLUSION

despite the low number of patients included in our study, SCA does not seem to be a risk factor for severe TB. What is Known: • Tuberculosis (TB) remains a global health problem particularly in developing countries, and Sickle cell anaemia (SCA) is currently one of the most common genetic diseases in the world that mainly affects African populations. • Very few data are available on TB in SCA patients. What is New: • The features of TB in children with SCA seem to be comparable to those expected in general population, with favourable outcomes in response to standard treatment. • Monitoring the dosage of anti-TB treatments could be of interest because of the possible impact of SCA on drug metabolism.

Ocular manifestations of sickle cell disease and genetic susceptibility for refractive errors

PURPOSE

Sickle cell disease (SCD) is the most common and serious form of an inherited blood disorder that lead to higher risk of early mortality. SCD patients are at high risk for developing multiorgan acute and chronic complications linked with significant morbidity and mortality. Some of the ophthalmological complications of SCD include retinal changes, refractive errors, vitreous hemorrhage, and abnormalities of the cornea.

MATERIALS AND METHODS

The present study includes 96 SCD patients. A dilated comprehensive eye examination was performed to know the status of retinopathy. Refractive errors were measured in all patients. In patients with >10 years of age, cycloplegia was not performed before autorefractometry. A subset of fifty patients' genotyping was done for NOS3 27-base pair (bp) variable number of tandem repeat (VNTR) and IL4 intron-3 VNTR polymorphisms using polymerase chain reaction-electrophoresis. Chi-square test was performed to test the association between the polymorphisms and refractive errors.

RESULTS

The results of the present study revealed that 63.5% of patients have myopia followed by 19.8% hyperopia. NOS3 27-bp VNTR genotypes significantly deviated from Hardy-Weinberg equilibrium (P < 0.0001). Although IL4 70-bp VNTR increased the risk of developing refractive errors, it is not statistically significant. However, NOS3 27-bp VNTR significantly reduced the risk of development of myopia.

CONCLUSION

In summary, our study documents the prevalence of refractive errors along with some retinal changes in Indian SCD patients. Further, this study demonstrates that the NOS3 VNTR contributes to the susceptibility to development of myopia in SCD cases.

Alteration of lymphocyte phenotype and function in sickle cell anemia: Implications for vaccine responses

Individuals with sickle cell anemia (SCA) have increased susceptibility to infections, secondary to impairment of immune function. Besides the described dysfunction in innate immunity, including impaired opsonization and phagocytosis of bacteria, evidence of dysfunction of T and B lymphocytes in SCA has also been reported. This includes reduction in the proportion of circulating CD4+ and CD8+ T cells, reduction of CD4+ helper: CD8+ suppressor T cell ratio, aberrant activation and dysfunction of regulatory T cells (Treg ), skewing of CD4+ T cells towards Th2 response and loss of IgM-secreting CD27 + IgM(high) IgD(low) memory B cells. These changes occur on the background of immune activation characterized by predominance of memory CD4+ T cell phenotypes, increased Th17 signaling and elevated levels of C-reactive protein and pro-inflammatory cytokines IL-6 and TNF-α, which may affect the immunogenicity and protective efficacy of vaccines available to prevent infections in SCA. Thus, in order to optimize the use of vaccines in SCA, a thorough understanding of T and B lymphocyte functions and vaccine reactivity among individuals with SCA is needed. Studies should be encouraged of different SCA populations, including sub-Saharan Africa where the burden of SCA is highest. This article summarizes our current understanding of lymphocyte biology in SCA, and highlights areas that warrant future research. Am. J. Hematol. 91:938-946, 2016. © 2016 Wiley Periodicals, Inc.

Antibody persistence after serogroup C meningococcal conjugate vaccine in children with sickle cell disease

BACKGROUND

A decline of protective antibody titers after MCC vaccine has been demonstrated in healthy children, this may be an issue of concern for risk groups. The aim of this study was to evaluate the persistence of bactericidal antibodies after MCC vaccine in sickle cell disease (SCD) patients. The type of vaccine used and booster response were also analyzed.

METHODS

SCD patients (n=141) previously immunized with MCC vaccines had blood drawn 2-8 years after the last priming dose. They were distributed according to age at primary immunization into groups: <2 years and 2-13 years and evaluated by years since vaccination (2-3, 4-5 and 6-8). Serum bactericidal antibodies with baby rabbit complement (rSBA) and serogroup C-specific IgG concentrations were measured. The correlate of protection was rSBA titer ⩾8. Subjects with rSBA <8 received a booster dose and antibody levels re-evaluated after 4-6 weeks.

RESULTS

For children primed under 2years of age rSBA titer ⩾8 was demonstrated in 53.3%, 21.7% and 35.0%, 2-3, 4-5, 6-8years, respectively, after vaccination, compared with 70.0%, 45.0% and 53.5%, respectively, for individuals primed at ages 2-13years. rSBA median titers and IgG median levels were higher in the older group. Six to eight years after vaccination the percentage of patients with rSBA titers ⩾8 was significantly higher in the group primed with MCC-TT (78.5%) compared with those primed with MCC-CRM197 [Menjugate® (33.3%) or Meningitec® (35.7%)] (p=0.033). After a booster, 98% achieved rSBA titer ⩾8.

CONCLUSION

Immunity to meningococcal serogroup C in SCD children declines rapidly after vaccination and is dependent on the age at priming. Booster doses are needed to maintain protection in SCD patients. Persistence of antibodies seems to be longer in individuals primed with MCC-TT vaccine comparing to those immunized with MCC-CRM197.

Transgenic sickle cell disease mice have high mortality and dysregulated immune responses after vaccination

BACKGROUND

Children with sickle cell disease (SCD) are susceptible to recurrent infections, which are often life threatening and necessitate frequent vaccinations. Given the altered baseline immunity and proinflammatory state associated with SCD, we sought to determine the relative safety and efficacy of vaccination in transgenic SCD mice.

METHODS

Eight-week-old SCD mice were vaccinated with ovalbumin and aluminum hydroxide weekly for 3 wk by the intraperitoneal or intramuscular route. One week after the third vaccination, serum cytokines/chemokines, immunoglobulins, and bronchoalveolar lavage fluid cytokines were measured.

RESULTS

Only SCD mice were prone to mortality associated with vaccination, as 40% of the animals died after the intraperitoneal vaccinations and 50% died after the intramuscular vaccinations. Serum IgG2b and IgM were significantly lower in SCD mice than in C57BL/6 mice after vaccination, but ovalbumin-specific IgE was significantly higher. Serum interleukin (IL)-1α, IL-2, IL-5, macrophage inflammatory protein 1α, and granulocyte macrophage-colony stimulating factor were significantly lower in SCD mice than in C57BL/6 mice after vaccination, whereas bronchoalveolar lavage fluid IL-1β and IL-6 were increased.

CONCLUSION

Mice with SCD appear to have a dysregulated immune response to vaccination. Thus, the relative safety and immunogenicity of vaccination should be studied in greater detail in the context of SCD.

Durable immune response to inactivated H1N1 vaccine is less likely in children with sickle cell anemia receiving chronic transfusions

BACKGROUND

Defects in the immune system may affect vaccine responsiveness. Because of the splenic hypofunction and abnormal opsonic activity, it was unknown whether patients with sickle cell disease (SCD) would respond appropriately to H1N1 vaccination. The objective of this study was to assess seroprotective post-vaccine H1N1 antibody response in children with SCD.

PROCEDURE

Serum antibody titers were measured by hemagglutination inhibition and microneutralization (MN) assays. Correlations were established between clinical and treatment parameters and immune response.

RESULTS

Twenty-nine of 38 (76.3%) subjects (mean age 11 ± 5.4 years) had durable protective antibody titers 8 ± 1.6 months (range 5-12 months) post-vaccination. Lessened immune response was not associated with time interval from vaccination, splenectomy, or hydroxyurea treatment. Lack of antibody response was associated with age less than 3 years and treatment with chronic transfusions. Of the nine non-responders, seven were on chronic transfusions (39% unresponsiveness rate in the transfused group). The difference in the number of patients with seropositivity between the non-transfused and the transfused groups was statistically significant (P = 0.039).

CONCLUSIONS

Most subjects were able to mount an influenza-specific antibody response against the inactivated H1N1 vaccine. Similar to the general population, children less than 3 years were less likely to respond. In addition, patients on chronic transfusions were less likely to respond when compared to non-transfused children. Clinicians should be aware of the possibility of decreased vaccine response in patients with SCD on chronic transfusions. We postulate that transfusion-related immunomodulation (TRIM) may be related to decreased response.

Splenic morphological changes are accompanied by altered baseline immunity in a mouse model of sickle-cell disease

Although functional asplenia from infarctions may be a major contributor to increased infectious mortality in sickle-cell disease (SCD), this relationship has not been fully defined. We used the transgenic Berkeley SCD mouse to define blood and splenic immunophenotypic differences in this model compared with C57BL/6 and hemizygous controls. In the serum of SCD mice, we found increased IgG2a and suppressed IgM, IgG2b, and IgA levels. Serum IL-6 levels in SCD mice were elevated, whereas IL-1α, CXCL10, and CCL5 levels were decreased. The blood of SCD mice had higher white blood cell counts, with an increased percentage of lymphocytes and decreases in other leukocytes. Immunophenotyping of lymphocytes revealed higher percentages of CD8(+) and T-regulatory cells and lower percentages of B cells. SCD mouse spleens exhibited histological disorganization, with reduction of defined lymphoid follicles and expansion of red pulp, a greater than fourfold increase in splenic mononuclear cells, marked expansion of the nucleated red blood cell fraction, and B-cell and CD8(+) T-cell lymphopenia. Within the splenic B-cell population, there was a significant decrease in B-1a B cells, with a corresponding decrease in IgA secreting plasma cells in the gut. Confocal microscopy of spleens demonstrated complete disruption of the normal lymphofollicular structure in the white pulp of SCD mice without distinct B, T, and marginal zones. Our findings suggest that altered SCD splenic morphological characteristics result in an impaired systemic immune response.

Cytokine levels and profiles in children related to sickle cell disease and asthma status

Atopic asthma in patients with sickle cell disease (SCD) is associated with an increased risk of acute chest syndrome (ACS). Cytokine-mediated inflammation might explain this association. Studies of cytokine profiles in patients with SCD have yielded conflicting data, but the possible influence of asthma status has not been examined. Our aim was to test the hypothesis that cytokine levels and profiles in SCD children reflected their asthma status. Samples from 155 Jamaican children (80 had SCD) and 64 British children (53 had SCD) who had their asthma status documented were analyzed for the presence and levels of interleukin 4 (IL-4) and interferon (IFN)-γ; they were also classified by their T helper cell (Th) cytokine profile. Jamaican children with SCD, when compared with Jamaican controls, were more likely to be diagnosed with asthma (P=0.001), more likely to be IL-4 positive (P<0.001), and more likely to be classified as having a Th-2 pattern (<0.001). In contrast, British children with SCD, when compared with the British controls, were less likely to have been diagnosed with asthma (P=0.04) and less likely to be classified as having a Th-2 pattern (P=0.006). Regression analysis demonstrated that amongst Jamaican children, SCD status, but not asthma status, ACS history, or gender, was predictive of IL-4 positivity and Th-2 status (P<0.001). In British children, none of those variables were significant predictors of IL-4 positivity or Th status. Cytokine profiles differed between Jamaican and British children. In the Jamaican children they reflected SCD, but not asthma or ACS status.

Susceptibility to invasive bacterial infections in children with sickle cell disease

Individuals with sickle cell disease (SCD) demonstrate an increased susceptibility to invasive bacterial infections (IBI). The most common organisms causing IBI are Streptococcus pneumoniae, nontyphi Salmonella species and Haemophilus influenzae type b (Hib). IBI are the most common causes of death in children below 5 years of age with SCD. Increased susceptibility to IBI is because of several factors including dysfunctional antibody production and opsonophagocytosis as well as defective splenic clearance. Early diagnosis of Hib and pneumococcal infections combined with antibiotic prophylaxis and immunization programs, could lead to significant improvements in mortality, especially in Africa.

Chlamydia pneumoniae and acute chest syndrome in patients with sickle cell disease

PURPOSE Few studies address the association of Chlamydia pneumoniae infection with pulmonary disease and outcome in patients with underlying pathology such as sickle cell disease (SCD). SCD patients are susceptible to the pulmonary disorder known as acute chest syndrome (ACS), where the etiology remains ill defined. The purpose of this study was to analyze the clinical course and outcome of C. pneumoniae-associated ACS among SCD patients as part of the National Acute Chest Syndrome Study.

PATIENTS AND METHODS

This was a longitudinal study of SCD patients presenting with ACS to multiple U.S. medical centers. Two hundred ninety-six SCD patients who developed ACS were tested by PCR for C. pneumoniae and by standard techniques for other respiratory pathogens. These infections were evaluated for association with ACS, clinical course, and complications.

RESULTS

Forty-one (14%) patients with first episodes of ACS were PCR positive for C. pneumoniae. Compared with other infections, C. pneumoniae-infected patients were older, were more likely to present with chest pain, and had higher hemoglobin levels at diagnosis. Both groups had similar rates of respiratory failure and prolonged hospitalization. Of the 89 patients with single-pathogen infections, 27 (30%) were due to C. pneumoniae, 21% to Mycoplasma pneumoniae, 10% to RSV, 4% to Staphylococcus aureus, and 3% to Streptococcus pneumoniae.

CONCLUSIONS

C. pneumoniae was the most prevalent pathogen in this study of ACS and was responsible for significant morbidity. Additional research is required to develop effective treatment guidelines for ACS.

[Severe infections in children with sickle cell disease: clinical aspects and prevention]

Sickle-cell disease (SCD) is associated with frequent and often severe infections as a result of immune function impairment and functional asplenia. Also, infection can trigger a vasoocclusive crisis. Pneumonococcal bacteremia and meningitis due to S. pneumoniae are often lethal and justify the penicillin prophylaxis, which has provided a dramatic decrease in early mortality bacterial pneumonia is common in patients younger than four years, with most cases being due to S. pneumoniae, H. influenzae, Mycoplasma pneumoniae, Chlamydia pneumoniae. Acute chest syndrome is both a difficult differential diagnosis and a common concomitant of bacterial pneumonia, because they are often intricated. Osteomyelitis is generally due to Salmonella, most often S. enteritidis. Multiple foci are common and treatment is difficult, with some patients developing chronic osteomyelitis with sequestration. Osteomyelitis is less frequent in developed countries and must been differentiated with bone infarction by use of bone scintigraphy. Parvovirus B19 infection causes acute erythroblastopenias. Malaria does not result in cerebral malaria, but can lead to severe anaemia or vasoocclusive crisis, and should therefore be effectively prevented. Antimicrobials are generally selected for efficacy against pneumococci (septicemia, meningitis), Salmonella (osteomyelitis, meningitis), and M. pneumoniae (pneumonia). Prophylactic therapy is of paramount importance and relies on long-term or lifelong penicillin therapy started at three months of age and no closely-spaced immunizations, most notably against peumococci, hepatitis B virus, S. typhi and H. influenzae. Resistant pneumococcal strains have not been reported to cause prophylactic treatment failures. New conjugated pneumococcal vaccines are effective in protecting very young infants and should therefore be used in sickle cell patients.

Alpha-2-macroglobulin and interleukin-6 levels in steady-state sickle cell disease patients

Endothelial activation and subclinical microvascular occlusions are an ongoing process during steady-state sickle cell disease, leading to interleukin production and an acute-phase response. Alpha-2-macroglobulin (alpha2M) is an acute-phase protein mainly regulated by interleukin-6 (IL-6). On the other hand, alpha2M acts as a carrier protein for IL-6 during inflammatory stress. The purpose of this study is to further assess the interactions between IL-6 and alpha2M as potent modulators of inflammatory reactions during the steady state of sickle cell disease. We measured alpha2M and IL-6 levels in 21 patients (12 male, 9 female; age range 12-44 years) in the steady state of sickle cell disease. Four patients had homozygous sickle cell anaemia and 17 had double heterozygous sickle cell/beta-thalassaemia. Diagnostic quantification of alpha2M was performed by rate nephelometry. Commercial enzyme immunoassay test kits were used for the quantitative measurement of IL-6. The alpha2M and IL-6 levels were compared to the values obtained from healthy volunteers. Mean values (+/- SD) of alpha2M and IL-6 were found to be significantly increased (p < 0.0005) in the patients (alpha2M: 337.2 +/- 104 mg/dl; IL-6: 4 +/- 2.1 pg/ml) compared to the healthy controls (alpha2M: 204.2 +/- 45.8 mg/dl; IL-6: 1.15 +/- 2.5 pg/ml). IL-6 values were positively correlated with alpha2M levels (r = 0.61, p < 0.01). We observed increased alpha2M and IL-6 levels in steady-state sickle cell disease and a positive correlation between these two inflammatory mediators. We suggest that alpha2M is a potent modulator of the inflammatory reaction and tissue repair mechanism during steady-state microvascular occlusions. Elucidating the role of alpha2M in sickle cell disease could lead to the development of novel strategies and therapies for preventing the harmful systemic or local effects of excess cytokine production.

Invasive pneumococcal disease in the immunocompromised host

A normal constituent of the human upper respiratory flora, Streptococcus pneumoniae also produces respiratory tract infections that progress to invasive disease at high rates in specific risk groups. The individual factors that contribute to the development of invasive pneumococcal disease in this distinct minority of persons, include immune (both specific and innate), genetic, and environmental elements. Specific defects in host responses may involve age, deficiencies in levels of antibodies and complement factors, and splenic dysfunction. Combinations of these immune defects contribute to the increased rates of invasive pneumococcal disease in patients with sickle cell disease, nephrotic syndrome, neoplasms, and underlying medical conditions such as diabetes and alcoholic liver disease. The number of risk factors are greatest and the rates of invasive disease are highest in patients with HIV-1 infection, which has emerged as a major risk factor for serious S. pneumoniae infection worldwide.

Serum interleukin-6 levels in the steady state of sickle cell disease

In patients with childhood sickle cell disease (SCD) serum interleukin-6 (IL-6) levels were measured during the steady (healthy) state of disease. The corresponding measurements were made in comparable healthy normal controls. Serum IL-6 levels were assessed via ELISA in 27 SCD patients and 19 controls. Results revealed significantly higher circulating levels of IL-6 in the SCD patients (60 +/- 7 pg/ml) compared with the healthy controls (12 +/- 5 pg/ml). IL-6 is a multifunctional cytokine that plays a central role in host defense mechanisms. The impact of high circulating levels of IL-6 may be deleterious to humoral and cell-mediated immune functions in SCD, with resultant heightened risk for morbidity.

Reduced levels of CD2+ cells and T-cell subsets in patients with sickle cell anaemia

Investigation of B lymphocytes and T-lymphocyte subsets in patients with homozygous sickle cell disease (SCD) who were not in crisis and who did not demonstrate infectious complications showed these cell populations to be abnormal. The proportion of total T cells (CD2+) was significantly reduced (P = 0.002) when compared with controls. B cells (CD19+) were significantly elevated in sicklers (P = 0.029). Helper/inducer (CD4+) and suppressor/cytotoxic (CD8+) cells were significantly reduced (P = 0.019 and P = 0.0001, respectively). The average ratio of T cells/B cells in SCD patients was 3.7:1, while controls showed a ratio of 7.2:1. Since patients with SCD are abnormally susceptible to severe infections, we discussed the implications of low levels of CD4+ and CD8+ cells and the consequent cytokine imbalance in SCD patients which may lead to impairment of immunity.