Human Immunity and Blood

The Fc fragment  of IgE bind to a receptor on mast cells which is involved in the allergic reactions.

All cells of the immune system originates in the bone marrow and they include myeloid (neutrophils, basophils, eosinpophils, macrophages and dendritic cells) and lymphoid (B lymphocyte, T lymphocyte and Natural Killer) cells which differentiate along distinct pathways.

It is the correct statement as on antigenic stimulation, the germinal centers accomodates large populations of B lymphocytes undergoing mitosis and plasma cells secreting antibodies.

The antigen-dependent responses occur in the secondary lymphoid organs, such as the spleen and lymph nodes.

Red blood cells are also known as RBCs, red cells, red blood corpuscles, haematids, erythroid cells or erythrocytes. In humans mature red blood cells are oval and flexible biconcave disks. They lack a cell nucleus and most organelles to accommodate maximum space for haemoglobin. Sickle cell disease is an inherited disorder in which red blood cell is abnormally shaped. This abnormality can result in painful episodes, serious infections, chronic anemia and damage to body organs.

Macrophages are cells produced by the differentiation of monocytes in tissues. Amoeboid movement is a crawling type of movement in which the cell forms temporary cytoplasmic projections called pseudopodia (false feet) towards the front of the cell. Leukocytes like phagocytes or macrophages of the lymph show amoeboid movements to engulf antigen or microbes and to immigrate in the circulatory fluid.

Pus is an exudate typically white-yellow, yellow or yellow-brown formed at the site of inflammation during infection. An accumulation of pus in an enclosed tissue space is known as an abscess whereas a visible collection of pus within or beneath the epidermis is known as a pustule or pimple. Neutrophils are very active in phagocytosing bacteria and are present in large amount in the pus of wounds.

Blood group O individuals do not have either A or B antigens on the surface of their RBCs. But their blood serum contains IgM anti-A and anti-B antibodies against the A and B blood group antigens. Therefore, an individual of blood group O can receive blood only from a group O individual, but can donate blood to individuals of any ABO blood group, i.e.,  A, B, O or AB. They are known as universal donors.

Neutrophils, eosinophils, basophils are granulocytes.

They contain many structures that are critical to stop bleeding. They contain proteins on their surface that allow them to stick to breaks in the blood vessel wall and also to stick to each other. They contain granules that can secrete other proteins required for creating a firm plug to seal blood vessel breaks. Also, platelets contain proteins similar to muscle proteins that allow them to change shape when they become sticky.

Lymphoid stem cells derived from the bone marrow develop into competent T-lymphocytes with a functioning T-cell receptor and co-receptor in the thymus gland.

In case of injury, the damaged endothelial cells lining the blood vessel release von Willebrand's Factor, which makes the surfaces sticky. The platelets start adhering to the surfaces of endothelial cells. This effect is called platelet adhesion.

This is an incorrect statement as the platelets bud off from megakaryocytes and never have a nucleus.

Immunoglobulins, also known as antibodies, are glycoprotein molecules produced by plasma cells (white blood cells). They act as a critical part of the immune response by specifically recognising and binding to particular antigens, such as bacteria or viruses and aiding in their destruction. 

The alternative pathway of the complement system is activated by direct contact with pathogen surfaces and involves Factors B and D, whereas the classical pathway involves C1 (C1q, C1r, C1s) and the lectin pathway involves mannose-binding protein.