A4 Cells of Innate Immunity and Their Features

Question 1

Basics

Answer 1

Antigen Binding: 
-Ab
-epitop
-C3b
-PAMP
Phagocytosis & Exocytosis
Inflammation
Presentation

Question 2

Lymphocyte

Answer 2

• The populations of lymphocytes cannot be differentiated using light or electron microscopes
• T helper-, cytotoxic or regulator cells are separated by determination of CD (Cluster of Differentiation)
Lymphocyte
CD: the set of monoclonal antibodies that recognize a single protein on a cell surface.

Question 3

B-lymphocyte

Answer 3

Antibody (Ab, immunoglobulin, Ig): a protein synthesized by an antigen exposure and produced by the immune system to recognise and eliminate that antigen.
• The Ab is produced by activated B-lymphocytes in the humoral immune response • Plasma cells produce them in high amounts • They consist of two heavy (H) and two light (L) chains, connected with S-S bridges through covalent bound • The N-terminal of the chains is variable, it is capable to bind the antigen specifically • The C-terminal takes part in an effector mechanism of the immune response

Question 4

Cells involved

Answer 4

• Phagocytic cells (granulocytes and macrophages)
• Dendritic cells
• Mast cells (release histamine)
• Natural Killer cells
• CD5+ of B-cells and ƴ/𝛿 (gamma/delta) of T cells (they will not react like B and T cells in the specific immune response, but they are present in the skin and MM where they react with atg and decides if they are harmful or not)

Question 5

Phagocytic cells

Answer 5

• Granulocytes
o Neutrophils: Phagocytosis and elimination of antigens using oxygen independent enzymes, like lysosomal enzymes e.g. superoxide dismutase.
▪ Multi-lobulated nucleus, vesicles are non-stained
▪ Are the first line of host defense, these cells fight the pathogens in the first place
▪ Lifespan: only 4-6 hours

o Eosinophils: Phagocytosis and modulate hypersensitivity by degrading/inactivating mast cell mediators
▪ Bilobed nucleus
▪ Most are present in the mucous membranes
▪ Granules: major basic protein

o Basophils: elimination of atg using lysosomal enzymes, histamine, serotonin and heparin.
▪ Bilobed nucleus (looks obscure when stained)
▪ Circulate in the blood, act like mast cells
▪ Life-span: few days (circulating cell does not divide)
▪ In the granules: histamine, heparin
▪ Important role in allergy.
• Macrophages: Phagocytosis by lysosomal enzymes, opsonisation, enzyme secretion

Question 6

Phagocytic cell receptor

Answer 6

1) PRR (pattern recognition receptor): located on the surface of the cells and will recognise PAMPs on the surface of atg.
2) ORR (opsonin recognition receptor): do not bind directly to the atg, but bind to the Ig produced by B cells, causing a structural change so that the atg can be connected to the cell. Most of the receptors in the complement system is this kind of receptor.

When a receptor of a phagocytic cell binds to an atg receptor (PRR and PAMP), the atg will be engulfed by the cell. The atg is broken down inside the phagocyte (but always enclosed in a vesicle to not come in contact with the interior of the cell), and a small fragment, usually a peptide, is presented on the cell surface in the MHCII complex (MHCI is for self presentation of proteins). The Th will recognise the MHCII presentation, and activate the specific immune response - hence, this is the link between the natural and specific immunity!

Question 7

Mast Cells

Answer 7

▪ Highest number occur where body is exposed to potential invaders e.g. airways, skin, intestines, blood vessels.
▪ Important role in allergy and inflammation.
▪ Contains many granules rich in histamine and heparin

Question 8

Dendritic Cells:

Answer 8

Antigen recognising and antigen presenting cells which are the connection between nonspecific and specific parts of the immune system as they present the antigen to the T cells.

Question 9

Natural Killer Cells:

Answer 9

cells which are a cytotoxic lymphocyte that is analogous to that of cytotoxic T cells in the specific immune system. Involved in MHC-1.