What is capsular polysaccharide antigen?
The capsular polysaccharide (CPS) constitutes the outermost layer of the bacterial cell and is the main virulence factor (Martens et al., 2004). This pathogen has a large number of different immunological types, differentiated by their CPS.
What is a capsular polysaccharide?
Capsular polysaccharides are highly hydrated molecules that are over 95% water [2]. They are often linked to the cell surface of the bacterium via covalent attachments to either phospholipid or lipid-A molecules, although some CPS may be associated with the cell in the absence of a membrane anchor [1, 3].
Can polysaccharides act as antigens?
Traditionally, polysaccharides were considered to be T cell-independent antigens that did not directly activate T cells or induce protective immune responses.
What do polysaccharide vaccines do?
Polysaccharide vaccines reduce the incidence of infection among military recruits, reduce the progress of epidemics of serogroup A disease and protect susceptible complement factor-deficient individuals. Capsule polysaccharide vaccines are available for the pathogenic meningococcal serogroups A, C, Y and W135.
Why are polysaccharide capsules important virulence factors?
Function. The capsule is considered a virulence factor because it enhances the ability of bacteria to cause disease (e.g. prevents phagocytosis). The capsule can protect cells from engulfment by eukaryotic cells, such as macrophages.
What is pneumococcal capsular polysaccharide?
The polysaccharide capsule of Streptococcus pneumoniae is the dominant surface structure of the organism and plays a critical role in virulence, principally by interfering with host opsonophagocytic clearance mechanisms.
Why is polysaccharide a poor antigen?
Thirdly, some bacterial polysaccharides are poor immunogens in humans due to their structural similarities with glycolipids and glycoproteins present in man. The T-lymphocyte independent nature of a polysaccharide may be overcome by conjugating the native or depolymerised polysaccharide to a protein carrier.
Why are polysaccharides not suitable for making antibody molecules?
Antibody Molecule They have a complex structure such as protein . Polysaccharides would not be suitable for making antibody molecules because there is no variety, it couldn’t be complimentary unlike proteins.
What is the difference between polysaccharide and conjugate vaccines?
In the polysaccharide vaccine, only the sugar part of the bacteria, the capsule, is included as the antigen to stimulate the immune response. “In the conjugate vaccine, it’s actually the sugar joined to the carrier protein,” says Associate Professor Kristine Macartney.
Do polysaccharide vaccines stimulate T cell mediated immunity?
Polysaccharide vaccines stimulate B-cell responses, thereby resulting in type-specific antibody production that enhances ingestion and killing of the pathogens by phagocytes. The antigens, however, are T-cell independent and therefore do not result in long-lasting immunity.
How does a capsule contribute to pathogenicity?
Bacterial Capsules and Host Defense. A primary function of capsules in pathogenic bacteria is to shield the bacterial surface from interactions with components of the host immune system and prevent either opsonophagocytosis or, in Gram-negative bacteria, complement-mediated lysis [17].
How do capsules contribute to virulence?
The capsule is considered a virulence factor because it enhances the ability of bacteria to cause disease (e.g. prevents phagocytosis). The capsule can protect cells from engulfment by eukaryotic cells, such as macrophages.
What is the importance of the capsule in pathology?
Capsules have a significant role in determining access of certain molecules to the cell membrane, mediating adherence to surfaces, and increasing tolerance of desiccation. Furthermore, capsules of many pathogenic bacteria impair phagocytosis (22, 29, 30) and reduce the action of complement-mediated killing (7, 31, 35).
What are three specific functions of capsules?
It has several functions: promote bacterial adhesion to surfaces or interaction with other organisms; act as a permeability barrier, as a defense mechanism against phagocytosis and/or as a nutrient reserve.
Is Streptococcus pneumoniae a polysaccharide capsule?
Does pneumococcal have capsule?
Streptococcus pneumoniae (the pneumococcus) is an important human pathogen. Its virulence is largely due to its polysaccharide capsule, which shields it from the host immune system, and because of this, the capsule has been extensively studied.
What are pure polysaccharide vaccines?
Pure polysaccharide vaccines are T-cell-independent activators of B-cells and their use usually results in an antibody only response (i.e., IgM). Polysaccharide–protein conjugate vaccines typically generate both humoral and cell-mediated immune responses.
How does the immune system response to encapsulated bacteria?
Figure 1: The immune response to polysaccharide and protein–polysaccharide conjugate vaccines. a | Polysaccharides from the encapsulated bacteria that cause disease in early childhood stimulate B cells by cross-linking the B-cell receptor (BCR) and drive the production of immunoglobulins.
Why are proteins more immunogenic than polysaccharides?
2). That is why proteins are more immunogenic than polysaccharides; they are chemically more complex. A microbe, such as a single bacterium, has many different proteins (and polysaccharides) on its surface that collectively form its various structures, and each different protein may have many different epitopes.