Diversity of age-dependent changes of antibody formation and of tolerance decrease

Acquired immunological tolerance in aged mice. II. The cellular basis of the loss of tolerance sensitivity

Aged C57Bl/6 mice (12 and 24 month) become resistant to tolerance induction with deaggregated human IgG (DHGG). The cellular basis for this tolerance resistance was investigated using adoptive transfer systems and challenged with endotoxin and antigen in the form of heat aggregated HGG. DHGG induced antigen specific suppressor cells in the spleens of aged mice although not in young mice and aged normal splenocytes were more sensitive to suppression. Low dose cyclophosphamide treatment to ablate suppressor cells did not curtail tolerance induction in aged animals. These observations coupled with the transient nature of B cell tolerance in aged mice suggest that the tolerance defect of senescence lies in the B cell compartment.

Acquired immunological tolerance in aged mice III. The contribution of lymphoid cells and their environments to the age related resistance to tolerance induction

Whether lymphoid cells or their environment are responsible for the decreased tolerogen sensitivity of aged mice was examined using an adoptive transfer system. Bone marrow cells from old (24 months), middle aged (12 months) and young adult mice (2 months) were equally sensitive to tolerance induction with deaggregated human immunoglobulin (DHGG) when they were transplanted into young lethally irradiated syngeneic hosts. Adoptively transferred splenocytes also showed no age related difference in tolerogen sensitivity. Thus, the age related difference seen in the intact animal is due largely to environmental factors acting on lymphoid cells in the aged animal. The role of lipopolysaccharide (LPS) as one such environmental factor affecting tolerance induction was investigated. LPS administered to aged mice produced greater polyclonal B cell activation and autoantibody formation than it did in young animals. When LPS was administered shortly after DHGG injection it converted the tolerogen to an immunogen with greater efficiency in aged animals.

Diversity of age-dependent changes of antibody formation and of tolerance decrease

Age-dependent changes in immune response and in tolerance occur at different rates in inbred mice of different genetic backgrounds. The change in tolerizability is connected with the change in the balance of the suppressor helper circuit; the change in B-cells, at least in C57BL/6 mice, appears to be also due to a regulatory change. Changes in immune responsiveness and tolerance inducibility appear to vary independently of one another.