Human Immunity and Blood

Diapedesis is the process by which leukocytes (white blood cells) squeeze through capillary walls to reach sites of infection. The other options are unrelated: diapanse is likely misspelled, diaphysis is bone shaft, diakinesis is a meiosis stage.

Agranulocytes are white blood cells without visible granules in their cytoplasm. They include lymphocytes and monocytes. Eosinophils, neutrophils, and basophils (options A, B, C) are all granulocytes.

In an allergic reaction, mast cells release histamines, which cause vasodilation and increased capillary permeability, leading to the inflammatory response.

IgG is the most abundant immunoglobulin in human serum, accounting for approximately 75 percent of all antibodies. It is the only class of antibody capable of crossing the placenta.

Brain is not involved in the elicitation of the immune system. Lymphoids organs (i.e. organs where maturation and proliferation of lymphocytes occurs) are involved in the elicitation of the immune system. Thymus, bursa of fabricus of birds and bone marrow are primary lymphoid organs whereas lymph nodes, spleen and mucosa associated lymphoid tissues such as tonsils, Peyer's patches, etc. are scondary lymphoid organs. 

The blood group which is a universal acceptor is AB because plasma from the AB blood type has no antibodies against the antigens of other types, it can be given to anyone without causing an immune reaction.

The key cells responsible for immunity in vertebrates are white blood cells called lymphocytes which arise from precursor (stem cells) cells in the bone marrow. B-lymphocytes or B-cells mature in bone marrow while T-lymphocyte or T-cell mature in thymus. 

Heparin is a naturally occurring anticoagulant produced by basophils and mast cells.[9] Heparin acts as an anticoagulant, preventing the formation of clots and extension of existing clots within the blood.

Mature mammalian red blood cells (erythrocytes) lack a nucleus to provide more space for hemoglobin, which carries oxygen.

White blood cells (leukocytes) are a key part of the immune system and produce antibodies to identify and neutralize pathogens.

Mature human red blood cells and platelets lack a nucleus, while white blood cells (leukocytes) contain a nucleus and nucleolus.

Receptor-mediated endocytosis (RME), also called clathrin-mediated endocytosis, is a process by which cells absorb metabolites, hormones, other proteins and in some cases viruses by the inward budding of plasma membrane vesicles, containing proteins with receptor sites specific to the molecules.

Individuals with blood type O do not have A or B antigens on the surface of their red blood cells, which is why they are considered universal donors.

Lymphocytes are white blood cells which provide immunity.

O blood group does not have any antigen, but possesses both A and B antibodies.