Capsules can protect a bacterial cell from ingestion and destruction by white blood cells (phagocytosis). While the exact mechanism for escaping phagocytosis is unclear, it may occur because capsules make bacterial surface components more slippery, helping the bacterium to escape engulfment by phagocytic cells.

The capsule is the pathogen’s most important determinant of virulence because it allows the bacterial cells to escape phagocytes in the lung. The B. anthracis capsule is composed of poly-D-glutamic acid. Its capsule is antiphagocytic, and it protects the bacteria from complement- mediated lysis in serum or blood.

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).

Capsules can resist unenhanced attachment by by preventing pathogen-associated molecular patterns or from binding to endocytic pattern-recognition receptors on the surface of the phagocytes. The capsules of some bacteria interfere with the body’s complement pathway defenses.

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. Among pathogens, capsule formation often correlates with pathogenicity.

The Steps Involved in Phagocytosis

• Step 1: Activation of the Phagocyte.
• Step 2: Chemotaxis of Phagocytes (for wandering macrophages, neutrophils, and eosinophils)
• Step 3: Attachment of the Phagocyte to the Microbe or Cell.
• Step 4: Ingestion of the Microbe or Cell by the Phagocyte.

1 Introduction. Phagocytic cells of the immune system consist predominantly of macrophages and neutrophils. These cells represent the major cellular effectors of nonspecific host defense and inflammation.

The peptide:MHC class II complex can be recognized by antigen-specific armed helper T cells, stimulating them to make proteins that, in turn, cause the B cell to proliferate and its progeny to differentiate into antibody-secreting cells.

Activation of B cells

1. A B cell becomes activated when its receptor recognizes an antigen and binds to it.
2. Most antigens are T-dependent.
3. Interaction with antigens causes B cells to multiply into clones of immunoglobulin-secreting cells.
4. The process just described takes place among the circulating B lymphocytes.

Terms in this set (5)

• antigen recognition-B cell exposed to antigen and binds with matching complementary.
• antigen presentation-B cell displays epitope, Helper T cell binds secretes interleukin.
• clonal selection= interleukin stimulates B cell to divide.
• differentiation=become memory or plasma cells.

B cells produce and secrete antibodies, activating the immune system to destroy the pathogens. The main difference between T cells and B cells is that T cells can only recognize viral antigens outside the infected cells whereas B cells can recognize the surface antigens of bacteria and viruses.

B-cells can connect to antigens right on the surface of the invading virus or bacteria. T-cells can only connect to virus antigens on the outside of infected cells. They form plasma cells and memory cells. They form killer, helper and suppressor cells.

Similarities between B cells and T cells Both B and T cells originate in the bone marrow. These cells are involved in adaptive immunity. They are a type of lymphocytes. The cells are nucleated and motile.

Both T cells and B cells receptors on their surface, known as BCR (B-cell receptor) and TCR (T-cell receptor). These surface receptors recognize and bind specific antigens present on pathogens and help the immune system to kill them. Thus, the correct answer is ‘last option.

T-cells are a type of white blood cell that work with macrophages. Unlike macrophages that can attack any invading cell or virus, each T-cell can fight only one type of virus. You might think this means macrophages are stronger than T-cells, but they aren’t.

Like T cells, B cells possess antigen-specific receptors with diverse specificities. Although they rely on T cells for optimum function, B cells can be activated without help from T cells.