Aging and lymphocyte subsets in the spleen and peripheral blood of the Sprague-Dawley rat

Male rat leukocyte population dynamics predict a window for intervention in aging

Many age-associated changes in the human hematopoietic system have been reproduced in murine models; however, such changes have not been as robustly explored in rats despite the fact these larger rodents are more physiologically similar to humans. We examined peripheral blood of male F344 rats ranging from 3 to 27 months of age and found significant age-associated changes with distinct leukocyte population shifts. We report CD25⁺ CD4⁺ population frequency is a strong predictor of healthy aging, generate a model using blood parameters, and find rats with blood profiles that diverge from chronologic age indicate debility; thus, assessments of blood composition may be useful for non-lethal disease profiling or as a surrogate measure for efficacy of aging interventions. Importantly, blood parameters and DNA methylation alterations, defined distinct juncture points during aging, supporting a non-linear aging process. Our results suggest these inflection points are important considerations for aging interventions. Overall, we present rat blood aging metrics that can serve as a resource to evaluate health and the effects of interventions in a model system physiologically more reflective of humans.

Our blood contains many types of white blood cells, which play important roles in defending the body against infections and other threats to our health. The number of these cells changes with age, and this in turn contributes to many other alterations that happen in the body as we get older. For example, the immune system generally gets weaker at fighting infections and preventing other cells from developing into cancer. On top of that, the white blood cells themselves can become cancerous, resulting in several types of blood cancer that are more likely to happen in older people.

Many previous studies have examined how the number of white blood cells changes with age in humans and mice. However, our understanding of this process in rats is still poor, despite the fact that the way the human body works has more in common with the rat body than the mouse body.

Here, Yanai, Dunn et al. have studied samples of blood from rats between three to 27 months old. The experiments found that it is possible to accurately predict the age of healthy rats by measuring the frequency of populations of white blood cells, especially a certain type known as CD25+ CD4+ cells. If the animals had any form of illness, their predicted age deviated from their actual age. Furthermore, while some changes in the blood were gradual and continuous, others displayed distinct shifts when the rats reached specific ages.

In the future, these findings may be used as a tool to help researchers diagnose illnesses in rats before the animals develop symptoms, or to more easily establish if a treatment is having a positive effect on the rats’ health. The work of Yanai, Dunn et al. also provides new insights into aging that could potentially aid the design of new screening methods to predict cancer and intervene using a model system that is more similar to humans.

Role of B1 and B2 lymphocytes in placental ischemia-induced hypertension

Preeclampsia is a prevalent pregnancy complication characterized by new-onset maternal hypertension and inflammation, with placental ischemia as the initiating event. Studies of others have provided evidence for the importance of lymphocytes in placental ischemia-induced hypertension; however, the contributions of B1 versus B2 lymphocytes are unknown. We hypothesized that peritoneal B1 lymphocytes are important for placental ischemia-induced hypertension. As an initial test of this hypothesis, the effect of anti-CD20 depletion on both B-cell populations was determined in a reduced utero-placental perfusion pressure (RUPP) model of preeclampsia. Anti-murine CD20 monoclonal antibody (5 mg/kg, Clone 5D2) or corresponding mu IgG2a isotype control was administered intraperitoneally to timed pregnant Sprague-Dawley rats on gestation day (GD)10 and 13. RUPP or sham control surgeries were performed on GD14, and mean arterial pressure (MAP) was measured on GD19 from a carotid catheter. As anticipated, RUPP surgery increased MAP and heart rate and decreased mean fetal and placental weight. However, anti-CD20 treatment did not affect these responses. On GD19, B-cell populations were enumerated in the blood, peritoneal cavity, spleen, and placenta with flow cytometry. B1 and B2 cells were not significantly increased following RUPP. Anti-CD20 depleted B1 and B2 cells in peritoneum and circulation but depleted only B2 lymphocytes in spleen and placenta, with no effect on circulating or peritoneal IgM. Overall, these data do not exclude a role for antibodies produced by B cells before depletion but indicate the presence of B lymphocytes in the last trimester of pregnancy is not critical for placental ischemia-induced hypertension.NEW & NOTEWORTHY The adaptive and innate immune systems are implicated in hypertension, including the pregnancy-specific hypertensive condition preeclampsia. However, the mechanism of immune system dysfunction leading to pregnancy-induced hypertension is unresolved. In contrast to previous reports, this study reveals that the presence of classic B2 lymphocytes and peritoneal and circulating B1 lymphocytes is not required for development of hypertension following third trimester placental ischemia in a rat model of pregnancy-induced hypertension.

Impact of moderate physical exercise--in comparison with dietary restrictions--on age-associated decline in cell-mediated immunity of Sprague-Dawley rats

BACKGROUND AND AIMS

Moderate physical exercise and dietary restriction have both been demonstrated to delay some of the adverse effects of aging. In order to elucidate similarities or dissimilarities in their mode of action on the aging immune system in a comparative setting, we examined significant parameters of cell-mediated immunity in Sprague- Dawley rats.

METHODS

Male Sprague-Dawley rats, housed individually, were divided into four groups, living from 5 months (baseline group BL) up to 15, 19 and 23 months of age as follows: voluntary running in wheels (RW), food restricted by feeding to pair weight with RW animals (PW), forced running on treadmills (TM), and sedentary controls with ad libitum access to food (S1). White blood cell counts, capacity for lymphocyte proliferation in response to Concanavalin A, and interleukin-2 (IL-2) plasma concentrations were determined.

RESULTS

White blood cell counts and the cell numbers of lymphocytes, neutrophil and eosinophil granulocytes were significantly lower in the older RW and PW groups. We observed influences of forced exercise on lymphocyte proliferation: blastogenic reactivity was higher in TM animals compared with RW and PW animals at 23 months of age. Exclusively for RW animals, we found lower plasma concentrations of IL-2 at 23 months.

CONCLUSIONS

Our data support the idea that moderate physical exercise modulates age-associated decline in the cell-mediated immunity of old Sprague-Dawley rats significantly more than corresponding dietary restrictions.

The effect of aerial parts of Echinacea on the circulating white cell levels and selected immune functions of the aging male Sprague-Dawley rat

Echinacea is one of the most widely used over-the-counter herbal preparations that purport to "improve immune system function", especially when taken as a short course of therapy (6-8 weeks). Since many purchasers are older individuals, a double-blind, placebo-controlled study was performed to investigate whether Echinacea could affect total and differential white cell counts, phagocytic activity and interleukin (IL-2) levels in 12-month-old, healthy, male Sprague-Dawley rats when administered over an 8-week period. Echinacea (50 mg/kg of aerial parts) mixed with peanut butter or peanut butter alone was fed to 16 rats, which were receiving regular food and water ad libitum. Cell counts and immune functions were determined on rat tail vein blood on a weekly basis. Echinacea significantly increased circulating total white cell counts during the first 2 weeks of administration, and IL-2 levels during the final 5 weeks of the study period (p<0.05). Differential counts were altered during the entire 8-week study, with mononuclear cells significantly increased to the detriment of granulocytes (p<0.05). No such changes were observed in animals given peanut butter alone. No difference was observed in phagocytic function between animals given Echinacea or peanut butter alone. These studies suggest that aerial components of Echinacea affect both mononuclear cell levels and circulating IL-2 levels in older animals.

Age-associated changes in the immune system of German shepherd dogs

In order to look into the ageing of the canine immune system we investigated age-related changes and associated gender-related differences in parameters of innate and acquired immunity in German Shepherd dogs. We obtained the following findings: white blood cell counts, peripheral blood lymphocytes, lymphocyte proliferative activity and interleukin-2 (IL-2) serum concentrations were significantly lower in the group of old animals, whereas the concentrations of gamma-globulins and the functional activity of the complement system were significantly higher in the elderly. Phagocytic and bactericidal activity of polymorphonuclear cells, as well as their 'killing function,' the serum cytokine-like activities of tumour necrosis factor-alpha and the plasma concentrations of immunoglobulin G, as well as of alpha- and beta-globulins, were not significantly affected by age, whereas natural killer-cell activity and the serum cytokine-like activities of IL-1 were significantly higher only in the group of female old animals. With regard to gender-related differences, lymphocyte proliferative activities as well as plasma concentrations of alpha-globulin were significantly higher in the group of female animals, whereas the absolute numbers of segmented neutrophils were significantly lower. Species analogies with regard to ageing as presumed to exist between man and laboratory rodents also seem to be applicable to the dog. The observed age-related changes in the canine immune system are probably among the main causes for the multimorbidity of old age, affecting life expectancy and mortality in the dog and should be recognized and considered by the attending veterinarian.

Characterization of cytokine production, screening of lymphocyte subset patterns and in vitro apoptosis in healthy and Alzheimer's Disease (AD) individuals

In order to investigate the possibility of whether or not the lymphocytes of patients with Alzheimer's Disease (AD) are in an activated state, blood mononuclear cells from 45 AD patients and 45 healthy age matched controls were immunophenotyped by measuring the expression of CD3, CD4, CD7, CD8, CD25, CD28, CD56 and HLA-DR by flow cytometry. Circulating and in-vitro-produced cytokines were also measured by ELISA tests. CD7 and CD8 were significantly decreased in AD patients (48.3% and 18.2%, respectively) when compared to healthy subjects (63.2% and 28.3%, respectively). A significant increase in the CD4, CD25 and CD28 antigen expression was also observed in the AD group (55.3% 24.8% and 65.1%) with respect to healthy subjects (44.5%, 10.3% and 54.3%). In addition there was a significant difference in the extent of apoptosis in lymphocyte culture, as measured by mean fluorescence intensity (MFI) of Fas antigen (CD95) expression on CD4+ T cells in 6 AD patients (MFI = 36% and 43%, by anti-CD3 and hyperthermia mediated-apoptosis, respectively) with respect to 6 healthy individuals (MFI = 24% and 31%, by anti-CD3 and hyperthermia mediated-apoptosis, respectively), as well as in T-cell proliferation assay. A decline of Fas antigen expression on CD8+ subset was observed in the AD group with both stimuli (19% and 28%) comparing to the control group (29% and 39%). No differences were observed on circulating cytokines and spontaneous in vitro production of proinflammatory interleukin 1beta (IL-1beta), Tumor Necrosis Factor-alpha (TNF-alpha), IL-6 and IL-10 cytokines. Lipopolysaccharide (LPS)-stimulated in vitro production of IL-1beta, TNF-alpha, IL-6 and IL-10 measured by a whole blood culture system was significantly higher in AD patients comparing to controls. Furthermore, the observed differences were more evident at late stages of disease. These findings suggest that immunological tests, based on lymphocyte immunophenotyping combined with pro-inflammatory cytokine determinations and measurement of apoptosis in peripheral blood might represent a useful tool to obtain more insight into the pathogenesis of AD and into the level of immune activation which could characterize the pathological state of lymphocytes from individual AD patients.