Human Immunity and Blood

Hemocytoblasts (pluripotent hematopoietic stem cells) are the precursor cells that give rise to all blood cells, including erythrocytes (red blood cells). Hemocytes and erythropocytes are not the correct precursor cell names.

Rheumatoid factor does indicate a poor prognosis when found in RA patients, correlating with extra-articular (non-joint) complications of RA such as nodules, lung disease and vasculitis as well as with severely affected joints.

A reticular cell is a type of fibroblast that synthesises type III collagen and uses it to produce reticular fibers. Reticular cells are found in many tissues including the spleen, lymph nodes and lymph nodules. They also direct B cells and T cells to specific regions within the lymphatic tissue.

The HLA-B27 test is primarily ordered to help strengthen or confirm a suspected diagnosis of ankylosing spondylitis (AS). Over 90% of affected individuals are HLA-B27 positive.

Fas ligand (CD178) is expressed on activated T cells. The interaction with FAS which is a protein on many cell types triggers enzymes to degrade the target cell DNA.

The ABO blood group system classifies human blood into four main types based on the presence or absence of A and B antigens: Type A (A antigen only), Type B (B antigen only), Type AB (both antigens), and Type O (neither antigen). This classification system is fundamental for safe blood transfusion.

This option is correct because CD 8 is a transmembrane glycoprotein present in suppressor T cells.

Blood type O, particularly O-negative, is called the universal donor because individuals with this blood type can donate red blood cells to people with any other blood type (A, B, AB, or O). This is possible because O-type blood lacks A and B antigens on red blood cells that would trigger an immune response. Blood types A, B, and AB each have specific antigens that make them incompatible with universal donation. The 'a' in the question appears to be a typo.

Red blood cells do not have nuclei and they live for approximately four months. They are made very fast in our bone marrow.

Blood is red in colour due to haemoglobin present in the red blood cells. Therefore, test tube A will show unusual colour of blood because of deficiency in red blood cells.

Heparin is a natural anticoagulant substance found in blood, produced by mast cells and basophils. It prevents blood clotting by inhibiting thrombin. Fibrinogen and thrombin are actually involved in blood clotting (coagulation), not preventing it. Globin is a protein component of hemoglobin and unrelated to clotting.

Fibrin is a fibrous protein involved in the clotting of blood and is non-globular. It is a fibrillar protein that is polymerised to form a mesh that forms a hemostatic plug or clot (in conjunction with platelets) over a wound site.

Blood group O lacks both A and B antigens on red blood cells. It is known as the 'universal donor' because the absence of antigens means it can be transfused to recipients with any blood type without causing an immune reaction.

Agglutination is the clumping of cells, most commonly observed in blood typing when antibodies react with antigens on red blood cells. It is a fundamental immunological reaction used in blood compatibility testing.

Complements C1 to C5 are activated during endotoxin inactivation.