Autostimulatory adherent cells in the spleen of aging mice: characterization in the syngeneic host-versus-graft reaction

Aging and the dendritic cell system: implications for cancer

The immune system shows a decline in responsiveness to antigens both with aging, as well as in the presence of tumors. The malfunction of the immune system with age can be attributed to developmental and functional alterations in several cell populations. Previous studies have shown defects in humoral responses and abnormalities in T cell function in aged individuals, but have not distinguished between abnormalities in antigen presentation and intrinsic T cell or B cell defects in aged individuals. Dendritic cells (DC) play a pivotal role in regulating immune responses by presenting antigens to naïve T lymphocytes, modulating Th1/Th2/Th3/Treg balance, producing numerous regulatory cytokines and chemokines, and modifying survival of immune effectors. DC are receiving increased attention due to their involvement in the immunobiology of tolerance and autoimmunity, as well as their potential role as biological adjuvants in tumor vaccines. Recent advances in the molecular and cell biology of different DC populations allow for addressing the issue of DC and aging both in rodents and humans. Since DC play a crucial role in initiating and regulating immune responses, it is reasonable to hypothesize that they are directly involved in altered antitumor immunity in aging. However, the results of studies focusing on DC in the elderly are conflicting. The present review summarizes the available human and experimental animal data on quantitative and qualitative alterations of DC in aging and discusses the potential role of the DC system in the increased incidence of cancer in the elderly.

Termination by early deletion of V beta 8 + T cells of aged mice in response to staphylococcal enterotoxin B

The changes in the T cell repertoire of aging BALB/c mice include an increase of V beta 8 + T cells, most of which have a relatively low density of T cell receptors (TCR). We investigated the response of V beta 8 + T cells to staphylococcal enterotoxin B (SEB), a superantigen from a common bacterium, the anamnestic response to which is thought usually to be part of the defense against infection. The injection of an amount of SEB optimum for V beta 8 + T cell proliferation in young mice induced little or no proliferative response in aged mice, and within one or two days they died in shock with apoptotic cells in the spleen, a sign of T cell-shock caused by SEB. Flowcytometry analysis (FCA) 15 h after SEB injection, when cell division had not yet started, revealed the loss of 90% of V beta 8 + T cells in the blood and of 50% in the spleen in mice of all ages tested. However, conspicuous in the remaining V beta 8 + T cells in the spleens of the young mice but not in those of the aged mice, was an increased cellular complexity, as shown by the fact that light was strongly side scattered in FCA, indicating intracellular re-organization. The remaining T cells in the young could include progenitors for the expanding population of V beta 8 + T cells. As seen in lethal shock, V beta 8 + T cells in the aged are not unresponsive to SEB in vitro. They responded to the antigen by increasing the amount of TCR up to the level of that in young mice, but without proliferation. The proliferation arrest of V beta 8 + T cells of aged mice was found to be an intrinsic defect in in vitro cell mixture experiments, in which they were cocultured with young spleen cells which provided a complete immune microenvironment. It was simultaneously found in vitro that most of the V beta 8 + T cells from aged mice disappeared after antigen stimulation and that their disappearance was prevented by the presence of spleen cells from young mice, although they still did not proliferate. Taken all together the findings suggest that V beta 8+ T cells in the aged are at the end state of maturation and terminate by apoptotic death, causing T-cell shock in response to SEB.

Development of autoreactivity and changes of T cell repertoire in different strains of aging mice

Physiological changes with increasing age are generally accompanied by disorders of immunity, including autoaggression which can be seen in some syngeneic host-versus-graft reactions provoked when responder and stimulator cells are of different ages. The magnitude of the response, however, varies with the strain of mice. Footpad injection of irradiated spleen cells from 1-year-old, but not from 2-month-old, BALB/c mice (H-2d) into syngeneic young mice evoked popliteal lymph node-swelling, but this was not the case in DBA/2 (H-2d) mice. Therefore, the generation of autoreactivity was thought to be closely related to the change of T cell repertoire with age in the former strain of mice. At around 1 year of age, when only a small reduction in T cell number was observed and when a slight increase in CD8+ T cells in the periphery caused the CD4/CD8 ratio to be lower than in young mice, the proportion of V beta 8+ cells in BALB/c mice started to increase, increasing from 16% in the young to 27% in 2-year-old mice (P < 0.01). On the other hand, V beta 6+ T cells remained at the same level as in young mice throughout life. The increasing fraction of V beta 8+ T cells was characterized by a low density of T cell receptors (TcR) and it was more conspicuous in the spleen than in the peripheral blood in mice more than 1 year of age. A shift to a TcR-low population in V beta 8+, T cells was followed in a few months by a shift in V beta 6+ T cells. Although both the change of T cell repertoire and development of autoaggression may be parameters of aging, no direct correlation was demonstrated between them in experiments with cross-hybrids and recombinant inbred strains of BALB/c and DBA/2 mice. Probably, the two parameters are genetically and independently controlled. All the data taken together indicate that T cells undergo V beta-TcR-restricted changes during their life history, depending on their genetic background.