Serum immunoglobulin (G, A and M) classes and IgG subclasses in sickle cell anaemia

Serum Immunoglobulin Levels in Children with Sickle Cell Disease: A Large Prospective Study

Over the past 3 decades, the pediatric department of the university Intercommunal Créteil hospital, a referral center for sickle cell disease (SCD), has prospectively evaluated immunoglobulin (Ig) levels in a cohort of 888 children with SCD, including 731 with severe sickle genotypes (HbSS and HbSβ⁰ thalassemia) and 157 with milder genotypes (HbSC and HbSβ⁺ thalassemia). We found consistent sickle genotype differences in levels of IgG and IgA, with increased levels of IgA and IgG in the severe versus milder genotype, from early childhood to late adolescence. Additionally, our results revealed a low serum IgM level, irrespective of sickle genotype. Finally, we found that IgA and IgG levels were significantly increased after therapeutic intensification with hydroxyurea but were stabilized in children receiving a transfusion program. The mechanisms contributing to these changes in Ig levels are unclear as is their clinical significance. We believe they should be further investigated.

The intriguing contribution of white blood cells to sickle cell disease - a red cell disorder

Sickle cell disease (SCD) is characterized by a point mutation that replaces adenine with thymidine in the sixth codon of the beta-globin gene, a unique morphological abnormality of red blood cells, vaso-occlusion with ischaemic tissue injury, and susceptibility to infections. Vascular lumen obstruction in SCD results from interaction of erythrocytes, leukocytes, platelets, plasma proteins, and the vessel wall. The disease phenotype is a product of various genes and environmental factors acting in concert with the protein lesion underlying the red cell anomaly. The severity of SCD increases with leukocyte count. The biological basis and therapeutic implications of this relationship are discussed. Leukocytes contribute to SCD by adhering to blood vessel walls and obstructing the lumen, aggregating with other blood cells with more effective blockage of the lumen, stimulating the vascular endothelium to increase its expression of ligands for adhesion molecules on blood cells, and causing tissue damage and inflammatory reaction which predispose to vaso-occlusion. Patients with impaired ability of leukocytes to kill microbes are more prone to infections; which precipitate sickle cell crisis. Reduction of leukocyte count ameliorates SCD. Similarly, targeted blockade or reduced synthesis of specific leukocyte adhesion molecules and their ligands might confer clinical benefit in SCD.

The management of crisis in sickle cell disease

The symptoms and signs of sickle cell disease are exacerbated in times of crisis, characterized by tissue infarction or worsening anaemia. Prompt medical intervention is required in these distressing situations to provide relief and comfort to the patient. Effective analgesia is crucial in treating the painful crisis of sickle cell disease. The haemoglobinopathy may cause hyposthenuria with reduced ability to excrete the sodium load in normal saline. A 5% dextrose solution or 5% dextrose in 25% normal saline is therefore recommended for intravenous hydration. As the leading cause of morbidity and mortality in sickle cell disease, infections call for vigorous antibiotic therapy. Oxygen administration should be reserved for hypoxic patients, and blood transfusion given only when really indicated. Acute chest syndrome and cerebrovascular accidents are life-threatening complications of sickle cell disease whereas priapism can cause important long-term sequelae; all deserve urgent attention. In the long term, comprehensive care is cost-effective in reducing the frequency and adverse effects of sickle cell crisis.

Role of immunoglobulin G subclasses in Q fever

The progression of Q fever to either acute or chronic disease has been attributed both to biological characteristics of the bacteria and to the host immune response. In order to determine whether a specific immunoglobulin G (IgG) subclass distribution could play a diagnostic or prognostic role in Q fever, IgG subclass levels were measured in patients with acute or chronic disease. It was observed that (i) IgG1 and IgG3 levels were elevated in patients with chronic Q fever compared to patients with acute disease or normal controls; (ii) variations over time reflected inverse complementary relationships of subclass levels, such as between IgG1 and IgG3 compared with IgG2 and IgG4, or an inverse relationship between IgG1 and IgG2; (iii) variations in IgG2 and IgG3 total subclass levels during follow-up of patients with chronic Q fever showed a decrease in IgG2 with a concomitant increase in IgG3 two years from disease onset. These findings indicate that measurements of IgG subclasses may be a simple, additional tool useful in the diagnosis of Q fever. This data raises the question of an unusual immunoregulatory mechanism in Q fever that is implicated in the presentation of the clinical disease.