Biomedical Laboratory Science

Saturday, September 7, 2019

A Primeview on Sickle Cell Disease !

Sickle cell disease (SCD) is a group of inherited disorders caused by mutations in HBB, which encodes haemoglobin subunit β. Haemoglobin molecules that include mutant sickle β-globin subunits can polymerize; erythrocytes that contain mostly haemoglobin polymers assume a sickled form and are prone to haemolysis. Other pathophysiological mechanisms that contribute to the SCD phenotype are vaso-occlusion and activation of the immune system. SCD is characterized by a remarkable phenotypic complexity. Common acute complications are acute pain events, acute chest syndrome and stroke; chronic complications (including chronic kidney disease) can damage all organs. Hydroxycarbamide, blood transfusions and haematopoietic stem cell transplantation can reduce the severity of the disease. Early diagnosis is crucial to improve survival, and universal newborn screening programmes have been implemented in some countries but are challenging in low-income, high-burden settings.

Sickle cell disease (SCD) is an umbrella term that defines a group of inherited diseases (including sickle cell anaemia (SCA), HbSC and HbSβ-thalassaemia) characterized by mutations in the gene encoding the haemoglobin subunit β (HBB). Haemoglobin (Hb) is a tetrameric protein composed of different combinations of globin subunits; each globin subunit is associated with the cofactor haem, which can carry a molecule of oxygen. Hb is expressed by red blood cells, both reticulocytes (immature red blood cells) and erythrocytes (mature red blood cells). Several genes encode different types of globin proteins, and their various tetrameric combinations generate multiple types of Hb, which are normally expressed at different stages of life — embryonic, fetal and adult. Hb A (HbA), the most abundant (>90%) form of adult Hb, comprises two α-globin subunits (encoded by the duplicated HBA1 and HBA2 genes) and two β-globin subunits.

A single nucleotide substitution in HBB results in the sickle Hb (HbS) allele βS; the mutant protein generated from the βS allele is the sickle β-globin subunit and has an amino acid substitution. Under conditions of deoxygenation (that is, when the Hb is not bound to oxygen), Hb tetramers that include two of these mutant sickle β-globin subunits (that is, HbS) can polymerize and cause the erythrocytes to assume a crescent or sickled shape from which the disease takes its name. Hb tetramers with one sickle β-globin subunit can also polymerize, albeit not as efficiently as HbS. Sickle erythrocytes can lead to recurrent vaso-occlusive episodes that are the hallmark of SCD. SCD is inherited as an autosomal codominant trait; individuals who are heterozygous for the βS allele carry the sickle cell trait (HbAS) but do not have SCD, whereas individuals who are homozygous for the βS allele have SCA. SCA, the most common form of SCD, is a lifelong disease characterized by chronic haemolytic anaemia, unpredictable episodes of pain and widespread organ damage.

This primeview focuses on SCA and aims to balance such remarkable advances with the key major challenges remaining worldwide to improve the prevention and management of this chronic disease and ultimately to discover an affordable cure.



Tuesday, June 4, 2019

Molecular Basis of Tolerance and Immunity to Antigens.

The intestinal immune system has to discriminate between harmful and beneficial antigens. Although strong protective immunity is essential to prevent invasion by pathogens, equivalent responses against dietary proteins or commensal bacteria can lead to chronic disease. These responses are normally prevented by a complex interplay of regulatory mechanisms. This article reviews the unique aspects of the local microenvironment of the intestinal immune system and discuss how these promote the development of regulatory responses that ensure the maintenance of homeostasis in the gut.

The intestinal immune system is the largest and most complex part of the immune system. Not only does it encounter more antigen than any other part of the body, but it must also discriminate clearly between invasive organisms and harmless antigens, such as food proteins and commensal bacteria. Most human pathogens enter the body through a mucosal surface, such as the intestine, and strong immune responses are required to protect this physiologically essential tissue. In addition, it is important to prevent further dissemination of such infections. By contrast, active immunity against non-pathogenic materials would be wasteful, and hypersensitivity responses against dietary antigens or commensal bacteria can lead to inflammatory disorders such as Coeliac Disease and Crohn's Disease, respectively. As a result, the usual response to harmless gut antigens is the induction of local and systemic immunological tolerance, known as oral tolerance. In addition to its physiological importance, this phenomenon can be exploited for the immunotherapy of autoimmune and inflammatory diseases, but it is also an obstacle to the development of recombinant oral vaccines. For these reasons, there is great interest in the processes that determine the immunological consequences of oral administration of antigen. To some extent, this discrimination between harmful and harmless antigens also occurs in other parts of the immune system, as it partly results from inherent properties of the antigen and associated adjuvants. Nevertheless, it has been proposed that there are also specific features of mucosal tissues that favour the induction of tolerance, the production of immunoglobulin A antibodies and, to a lesser extent, T helper 2 (TH2)-cell responses. Several features of mucosal tissues might contribute to these effects, including a unique ontogeny and anatomical patterning, specialized cells and organs that are involved in the uptake of antigen, distinctive subsets of antigen-presenting cells (APCs) and several unusual populations of B and T cells. In addition, the migration of lymphocytes to the intestine is controlled by a series of unique adhesion molecules and chemokine receptors.

This review article discusses the anatomical factors which determine the special nature of small intestinal immune responses, and the unique processes and cells involved in the uptake and presentation of antigen to T cells in the gut. In particular, it focuses on the local factors that determine the behaviour of APCs and T cells in the gut and discuss recent evidence that challenges the conventional dogma that Peyer’s patches are the only site for the initiation of mucosal immunity and tolerance.

It also focuses on the small intestine, as this tissue has been studied in most detail and it contains the largest proportion of immune cells in the gut. However, the reader should be aware that each compartment of the intestine, from the oropharynx to the stomach and to the rectum, has its own specializations, which might have individual effects on immune regulation in response to local antigens.
  • The intestinal immune system is an anatomically and functionally distinct compartment, in which a careful distinction must be made between harmful antigens, such as invasive pathogens, and harmless antigens, such as dietary proteins or commensal bacteria.
  • The default response to harmless antigens is the induction of tolerance. A breakdown in this physiological process can lead to disease.
  • Immune responses and tolerance in the gut are initiated in organized lymphoid organs, such as the Peyer's patches and mesenteric lymph nodes (MLNs). The mucosa contains effector or regulatory cells that migrate there selectively, from the MLNs, in the lymph and bloodstream under the control of α4β7 integrins and the chemokine receptor CCR9.
  • Pathogens might enter the intestinal immune system through M cells in the follicle-associated epithelium of the Peyer's patches, whereas soluble antigens might gain access predominantly through the normal epithelium that covers the villus mucosa.
  • Peyer's patches, lamina propria and MLNs contain unusual populations of dendritic cells (DCs), some of which are characterized by the production of interleukin-10 (IL-10) and which polarize T cells to an IL-4-, IL-10- and transforming growth factor-β (TGF-β)-producing 'regulatory' phenotype.
  • Genetically determined factors, together with luminal bacteria, might act on epithelial and stromal components of the intestinal mucosa to produce a local microenvironment that is dominated by the constitutive production of prostaglandin E2 (PGE2), TGF-β and IL-10. Under physiological conditions, this favours the differentiation of regulatory DCs and T cells, which leads to systemic tolerance and/or immunoglobulin-A production.

Wednesday, March 27, 2019

How to Increase Laboratory Accuracy with Direct HbA1c Testing !

Diabetes is a global epidemic affecting in the region of 425 million people according to the International Diabetes Federation. Worryingly, this figure is on the rise with forecasts suggesting diabetes will affect up to 629 million people globally by 2045. Such a dramatic increase highlights the fundamental need for better disease management. When we look at the worldwide prevalence of diabetes, the United States is one of the most prominent countries affected.

HbA1c - an important biomarker for diabetes management and control !

HbA1c, also known as hemoglobin A1c or glycated hemoglobin, is an important blood test used to determine how well diabetes is being controlled. It develops when hemoglobin, a protein within the red blood cells that carries oxygen throughout the body, joins with glucose in the blood, becoming “glycated.” The concentration of HbA1c in the blood of diabetic patients increases with rising blood glucose levels and is representative of the mean blood glucose level over the preceding six to eight weeks. HbA1c can therefore be described as a long-term indicator of diabetic control, unlike blood glucose which is only a short-term indicator of diabetic control. It is recommended that HbA1c levels are monitored every three to four months.


Tuesday, February 12, 2019

Pre-Med and Key Requirements for a Medical School !

What is pre-med? When people say that they’re pre-med, what does that actually mean? If you’re planning to attend a med-school and become a doctor, it’s important that you understand the definition of pre-med and what you should be doing as a pre-med student.

Read on to learn what it really means to be a pre-med, what you should be focusing on to get into med school, and what the best majors for pre-meds are and why.

What Does Pre-Med Mean?

“Pre-med” is the term people use to show that they want to go to a med-school and are taking the classes they need to get there. It’s primarily used by college students. There isn’t actually a major called “pre-med;” pre-med is just a term to let people know you have plans to be a doctor. You can be a biology major and a pre-med, a Spanish major and a pre-med, etc.

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