Characterization of the Hepatic and Splenic Immune Status and Immunoglobulin Synthesis in Aged Male Mice Lacking the Peroxisome Proliferator-Activated Receptor-Alpha (PPARα)

It is now well established that the nuclear receptor peroxisome proliferator-activated receptor-alpha (PPARα) is expressed in different types of immune cells and plays a pivotal role in the regulation of age-related production of inflammatory cytokines. However, the role(s) of this receptor in the regulation of immune cell homoeostasis in ageing non-lymphoid and lymphoid organs has not yet been resolved. We examine this issue here by evaluating the hepatic and splenic immune status and immunoglobulin (Ig) production in male PPARα-null mice and their wild-type littermates at one and 2 years of age. In comparison with the age-matched control animals, PPARα-null mice exhibited age-related elevations in the numbers of total, as well as of phenotypically distinct subpopulations of intrahepatic immune cells (IHIC) and splenocytes. Moreover, at 2 years of age, these alterations in hepatic immune cells were accompanied by significant increases in hepatic levels of the pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and interferon-gamma (IFN-γ), in combination with the development of hepatic inflammatory loci containing mixtures of leucocytes. Alterations in splenocytes of old PPARα-null mice were also accompanied by increases in cellularity of both white and red pulps of the spleen. Furthermore, these same animals exhibited pronounced increases in the numbers of splenic plasma cells and enhanced production of Ig of different isotypes, including IgG1, IgG2a and IgE. Thus, our findings indicate that upon ageing, PPARα plays a crucial role in regulating the total numbers, compositions and functions of immune cells in both lymphoid and non-lymphoid immune organs of mice.