Bacteria are the cause of many infectious diseases. They are prokaryotic microorganisms which can live on the body surfaces, in extracellular spaces, in cellular vesicles or in the cytosol.

Basedov's Disease is an autoimmune disease in which antibodies against the receptor for the thyroid stimulating hormone (TSH) are formed. This leads to the production of excess thyroid gland hormones and an illness called hyperthyroidism.

B cells or B lymphocytes are one of the two most important classes of lymphocytes. The antigen receptor of the B lymphocytes, also known as B cell receptor, is a cell surface immunoglobulin. If B cells are activated by contact with an antigen, they differentiate to plasma cells which shape antibodies with the specificity of the original receptor.

Blood-brain barrier: The brain is especially well protected by the blood-brain barrier. It normally prevents dangerous substances in the blood from harming the brain.

Blood platelets are small cell fragments formed from megakaryocytes which play an important role in the coagulation of the blood.

Blood poisoning (sepsis): Sepsis is an infection of the blood which often ends fatally. An infection with gram negative bacteria often results in a so-called septic shock from the release of the cytokine TNF .

Blood type antigens are surface molecules of the red blood cells which can be identified with the help of antibodies from other individuals. The most important blood type antigens are called ABO and Rh (Rhesus factor). They are used for typing blood in blood banks. There are also many other blood type antigens which can be detected using a cross sample.

Bone marrow: The cellular components of the blood are formed in the bone marrow. They include the erythrocytes, monocytes, polymorphonuclear leukocytes and blood platelets. This is also where B cells mature in mammals. In addition, it is the origin of the stem cells which migrate to the thymus gland and mature there into T cells. So a bone marrow transplant can restore all cellular elements of the blood, including those which are necessary for an acquired immune response.