The large intestine (colon) has a large resident population of microbiota, consisting of at least 1012 organisms per gram of luminal contents. These organisms, together with the antigenic load provided by the diet and the constant threat of potential pathogens, means the intestinal immune system encounters more antigen than any other part of the body.
The lung encounters a myriad of, potentially foreign, particles on a daily basis. As such, immune cells in this site must gauge whether or not to respond. This choice is partially removed by physical and soluble barriers to infections. Large particles are deposited in the nasopharynx and tonsillar regions and cleared by inertial forces (coughing and sneezing).
The oral cavity is a unique anatomical structure, characterised by the juxtaposition of soft and hard tissues and which is continuously subject to challenge by the external environment and foreign material. Diseases and disorders caused by oral microorganisms are very common and economically important, in particular dental caries (loss of tooth integrity caused by bacteria-derived organic acids) and periodontitis (‘gum disease’; chronic destructive inflammation of the supporting tissues of the teeth caused by anaerobic bacteria).
There are numerous small salivary glands within the tongue, lips cheeks and palate. Humans also have four large glands termed the parotid, submaxillary, submandibular and sublingual salivary glands. Collectively, the primary function of these glands is the production and secretion of saliva.
The intestine is home to about 100 trillion (1×1014) bacteria, both commensal (“friendly”) and pathogenic. To fight infection quickly the intestine has several innate immune defences designed to act immediately when alerted to danger.
Stem cell transplantation (SCT) is widely used to treat haematological malignancies such as lymphomas, multiple myeloma and myeloid/lymphoblastoid leukaemias. It is potentially applicable as a treatment for some solid organ tumours such as breast cancer and renal cell carcinoma, and is increasingly used to treat non-malignant conditions.
Transplants that are from a genetically unrelated donor of the same species are termed allografts. Allogeneic transplantation is deemed the last resort for the treatment of chronic organ failure. Even with the aid of organ preservation and the advances in immunosuppression, the major complication post-transplantation is rejection. Rejection occurs despite pre-transplant tissue typing/blood analysis and is seen in almost all transplant recipients, to varying degrees.
