LAUSR

ABSTRACT Susceptibility and declined resistance to human pathogens like respiratory syncytial virus (RSV) at old age is well represented in the cotton rat (Sigmodon hispidus). Despite providing a preferred model of human infectious diseases, little is known about aging of its adaptive immune system. We aimed to define aging‐related changes of the immune system of this species. Concomitantly, we asked whether the rate of immunological alterations may be stratified by physiological aberrations encountered during aging. With increasing age, cotton rats showed reduced frequencies of T cells, impaired induction of antibodies to RSV, higher incidence of aberrations of organs and signs of lipemia. Moreover, old animals expressed high biological heterogeneity, but the age‐related reduction of T cell frequency was only observed in those specimens that displayed aberrant organs. Thus, cotton rats show age‐related alterations of lymphocytes that can be classified by links with health status. HighlightsT cells and B cells defined in aging cotton rats.Cotton rats show increased interindividual biological variation at old age.Reduced T cell frequencies at old age are linked to signs of pathology.Signs of declining health may help classifying the rate of immunological aging.