Ageing lymphoid tissues

One component of the age-ielated decline in immune function is decreased production of the lymphokine that promotes the growth of T-ceUs, interleukin 2 (IL-2). Administration of recombinant-derived IL-2, both in vitro and in vivo, appears to restore certain immune functions in aged mice. Recovery of T-regulatory effects on B-ceU differentiation has been reported in human cells from elderly patients treated with IL-1 and/or IL-2 (42). Similar effects have been observed in the presence of the pentapeptide thymopentin [69558-55-0] (Arg Lys Asp Val Tyr), a weU-known IL-2 inducer. Recombinant IL-2 adrninistered to aged mice for three weeks has been shown to correct the T-ceU functional deficiency associated with antigen-specific immunoglobulin production by certain lymphoid tissue (43). 

Salmonella all ages/travelers to tropics 6-48 h moderate volume, and usually without blood mucosal invasion via M cells or enterocytes - macrophages and lymphocytes in Peyer s patches and other lymphoid tissue - bloodstream... 

In addition to thymic involution, there are other important age-associated changes in the structure of the lymphoid tissues. The number of mature lymphocytes and plasma cells in the bone marrow markedly increases while the number of germinal centres in the lymph nodes and spleen is reduced with age (Benner et al. 1981, Gonzalez-Fernan-DEZ et al. 1994). 

Cancer is uncommon during the first two decades of life, but is nonetheless a substantial concern. In the United States, cancer is diagnosed in approximately 12 400 children and adolescents annually and is the most common cause of death from any kind of disease between 1 and 19 years of age. In the United States and other developed countries, lymphoid neoplasms (leukaemia, lymphoma) and cancers of the central nervous system are the most common paediatric malignancies. Other kinds of childhood tumours include embryonal tumours of the retina, sympathetic nervous system, kidney, and liver tumours of bone and soft connective tissues and certain gonadal neoplasms. Different kinds of cancer (e.g. carcinomas of liver or thyroid) may predominate in children in parts of the world where specific environmental risk factors are more prevalent. 

The lymphoid system of the amphibians is more complex than that of fishes. In addition to a well-defined thymus gland, primitive lymph node tissue is also present (Kent et al., 1964). In frogs and toads for the first time marked seasonal changes in thymic size are noted (Dustin, 1911). Reptiles have a lymphoid system that is quite similar to that seen in amphibians, including a well-developed thymus that also involutes with age (Dustin, 1911). 

Bone Marrow. It is very important to check multiple sites, such as the head of the femur, the shaft of the femur, and the vertebral bodies, as the amount of hematopoietic tissue in each of these sites is often different. Also, there are species differences in the relative proportion of fat to hematopoietic tissue that changes with age and location. Careful comparisons to age- and sex-matched control animals, and inherent species-specific degrees of normal variability are vital for making accurate statements concerning compound-induced changes. Also, since the bone marrow is a site of erythroid, as well as lymphoid progenitors, any alteration of cellularity needs identification of the cell type involved, if possible. 

---