Brain-reactive antibodies in sera of aging non-human primates

Physical Activity and Cognitive Function among Older Adults with an Elevated Gamma Gap

OBJECTIVE

An elevated gamma gap is indicative of high serum concentrations of globulin proteins, some of which elicit acute inflammatory responses. An impaired cognitive function has been linked to central and peripheral inflammation, while exercise is associated with protective, anti-inflammatory benefits. In this study, we evaluated whether the gamma gap is associated with cognitive function among older adults and whether physical activity is favorably associated with cognitive function among those with an elevated gamma gap.

MATERIALS AND METHODS

Data from the 1999-2002 National Health and Nutrition Examination Survey (NHANES) were used to identify 2,352 older adults aged between 60 and 85 years. The gamma gap was evaluated by subtracting albumin from total protein, i.e., gamma gap = total protein (g/dL) - albumin (g/dL). Those at or above 3.1 g/dL (31.0 g/L) were considered to have an elevated gamma gap. The Digit Symbol Substitution Test (DSST) was used to assess cognitive function tasks of pairing and free recall among participants. Participants were asked open-ended questions about participation in leisure-time physical activity over the previous 30 days.

RESULTS

Those with an elevated gamma gap (DSST, 44.8) had a lower cognitive function score when compared to those without an elevated gamma gap (DSST, 50.1) (p < 0.001). After adjustments, and among those with an elevated gamma gap, those meeting the moderate-to-vigorous intensity physical activity (MVPA) guidelines (vs. not meeting them) had a DSST score of 6.42 units higher (β = 6.42, 95% CI 3.85-8.99, p < 0.001).

CONCLUSION

In this national sample of older adults, the gamma gap was associated with cognitive function, and among those with an elevated gamma gap, meeting the physical activity guidelines was associated with a higher cognitive function. Relevant clinical implications are discussed, as the gamma gap may be predictive of the risk for early mortality and reduced quality of life. Experimental work is needed to investigate whether physical activity training programs are effective in reducing an elevated gamma gap and preserving optimal cognitive functioning among at-risk individuals.

Animal models of age-related dementia: neurobehavioral dysfunctions in autoimmune mice

The development of strategies for treatment of Alzheimer's disease and other age-associated dementias is an important goal of research in the neurosciences. It is suggested that advances in understanding of the etiology of those disorders would provide the most obvious avenues to development of preventative treatments. Research findings from both clinical investigations and studies of animal models are presented which suggest a neuroimmunologic component in age-associated dementia. Clinical studies suggest an association between dementia and brain-reactive autoantibodies in subsets of patients with Alzheimer's disease. Studies of mice suggest that: 1) when compared with normal genotypes, mutant mice with accelerated autoimmunity show learning and memory impairments at earlier chronological ages; 2) the learning and memory deficits of autoimmune and normal mice are qualitatively similar; 3) the behavioral deficits of normal aged and autoimmune mice are sensitive to similar pharmacologic interventions. Overall, these findings suggest that intervention strategies targeting the immune system might be useful in the treatment or prevention of aging-associated dementia. Autoimmune mice would be useful as models for the development and testing of such immune-based interventions.

Studies on age-related functional changes in regulatory T cells and B cells involved in the autoantibody production of MRL/MpJ- +/+ mice

Age-related changes in anti-DNA autoantibody production of MRL/MpJ- +/+ mice were investigated. In lipopolysaccharide (LPS)-stimulated cultures, spleen cells of the mice showed an age-related, marked increase in the ability to produce IgG class of the autoantibody after the age of 12 months, while they showed a tendency to decrease with age in the production of IgM class of the autoantibody. Serum levels of anti-DNA autoantibodies rose markedly in the IgG autoantibody but not in the IgM autoantibody after 12 months of age, which is well consistent with the observation in the LPS-stimulated cultures. T cell-depleted spleen cells, however, showed only a small increase with age in the IgG autoantibody productive ability. These results suggest that the age-associated increase in the IgG autoantibody production in the mice is under T-cell control. Age-associated changes in suppressor capacity in spleen cells of the mice were also investigated. Suppressive activity of the cells stimulated by 2-day incubation with concanavalin A (Con A) showed a clear increase as the donor age advanced, when assayed on the LPS-stimulated anti-DNA autoantibody production in vitro. The results indicate that, in MRL/MpJ-+/+ mice, suppressor capacity does not decline with age and is not related as a cause to the autoantibody production.

herpes simplex virus infection accelerates the age-related reactivity of mouse trigeminal ganglia neurons with anti-mouse IgG antibody in immunostaining

The detection of viral proteins is a major goal of research on herpes simplex virus type 1 (HSV-1) latency. We used immunostaining to detect viral proteins in neuronal cells of trigeminal ganglia of Balb/c mice after corneal inoculation with HSV-1 virus. Viral proteins were detected in the neurons during the acute stage of infection, i.e. within one week after inoculation. However, the detection of viral antigens at the latent stage of HSV-1 infection has proven difficult. We have detected age-dependent non-specific reactivity with anti-mouse IgG antibody in the neurons of 10-week-old or older uninfected mice. This reactivity is accelerated in HSV-1 infected mice, being seen at 6 weeks of age (2 weeks post infection). The accelerated reaction and impact of this effect is discussed in relation to detection of viral proteins during latency.

Autoimmunity and age-associated cognitive decline

It is suggested that the immune system may play a role in the etiology of age-associated cognitive decline and/or Alzheimer's disease. The relationship between brain-reactive antibodies (BRA) and age-associated cognitive dysfunction is reviewed and discussed. A parallel relationship between BRA increases with age and decline of avoidance learning capacity is described in mouse models. Transfer of immunity from old to young mice was found to accelerate both age-related formation of brain-reactive antibodies and age-related decline of avoidance learning capacity. Short-lived mouse genotypes with accelerated autoimmunity were found to show accelerated age-related declines in their ability to acquire an avoidance response when compared with nonautoimmune mice. Overall, these findings suggest that the immune system could be an important target for development of intervention strategies aimed at extending the intellectually competent period of life. Mice in which autoimmunity is accelerated may be useful as models for the development of such interventions.

Age differences in acquisition and retention of one-way avoidance learning in C57BL/6NNia and autoimmune mice

Acquisition and 48-h retention of a step-up active avoidance response were studied in separate age groups of C57BL/6NNia mice (aged 1.5, 3.5, 6, 12, or 26 months) and five strains of genetically autoimmune mice differing in life span. The C57BL/6NNia mice showed no change in ability to acquire the avoidance response between 1.5 and 3.5 months, but showed a steady decline in that ability thereafter. Mouse strains with early-onset autoimmune disorder (NZB/B1NJ, MRL/MpJ-lpr, and BXSB/MpJ) showed declines in acquisition capability between 1.5 and 3.5 months of age, whereas mouse strains with mild, late-onset autoimmune disorder (MRL/MpJ- + and NZBWF1/J) showed stable or improved acquisition during that period. Both the C57BL/6NNia and NZB/B1NJ mice showed age-dependent declines in 48-h retention performance by 12 months of age. These findings suggested that while 48-h retention performance deficits were most related to chronological age, avoidance acquisition deficits were related to development of autoimmunity.

Motor responses of autoimmune NZB/B1NJ and C57BL/6Nnia mice to arecoline and nicotine

In 11-13 month C57BL/6Nnia mice, arecoline produced a dose-dependent decrease in motor activity at doses of 0.64-2.5 mg/kg, whereas at doses of 5.0-20.0 mg/kg arecoline produced a dose-dependent increase in motor activity. In marked contrast, age-matched NZB/B1NJ (New Zealand Black) mice failed to exhibit the first phase of the response, but showed a greater dose-dependent increase in motor activity following the doses of 10 and 20 mg/kg. Nicotine, 0.64-2.5 mg/kg, produced a dose-dependent decrease in motor activity in both strains. The effects of arecoline and nicotine were antagonized by scopolamine (2.5 mg/kg) and mecamylamine (1.0 mg/kg), respectively. These findings suggest that muscarinic neurotransmission may be altered in NZB/B1NJ mice, which produce brain-reactive autoantibodies, exhibit learning/memory dysfunctions, and also exhibit a loss of neurons staining positive for choline acetyltransferase.

Differences in behavioral responses to oxotremorine and physostigmine in New Zealand black (NZB/BlNJ) and C57BL/6 mice

The NZB/BlNJ (NZB) mice are an autoimmune-prone strain, known to develop brain-reactive antibodies in serum at much earlier chronological ages than normal mice. Measurement of locomotor activity in 8-10 month old C57BL/6 (C57) mice following the administration of either oxotremorine or physostigmine, revealed a biphasic response consisting of inhibition at small doses, but increased motor activity at large doses. In contrast, age-matched NZB mice exhibited little inhibition at the smaller doses, but had much greater increases in activity after the larger doses. Similarly, when compared to C57 mice, NZB mice were less sensitive to oxotremorine-induced salivation, diarrhea and visible tremors. Moreover, oxotremorine-induced hypothermia occurred at smaller doses in C57 mice than in NZB mice and was of a greater magnitude. Thus, at an age when NZB mice possess high levels of brain-reactive antibodies, and exhibit impairment in tests of learning/memory, these mice also show diminished responses in several tests of cholinomimetic-induced behavior and physiological alterations.

Learning deficits occur in young mice following transfer of immunity from senescent mice

The extent to which immune processes contribute to senescence-related neurological/behavioral impairment was examined using an adoptive transfer procedure. C57BL/6 mice aged 22 to 24 months showed impaired ability for acquisition of an active avoidance response when compared with younger mice aged 3 months. An immunofluorescence assay of the sera of these mice indicated that only sera from the senescent mice reacted with brain antigen. When tested three months following irradiation and receipt of bone marrow/spleen cell suspensions from senescent mice, young mice showed senescence-like serum-brain reactivity and declines in their abilities to acquire learning. Young control mice receiving cell suspensions from age-matched donors showed no evidence of serum-brain reactivity or learning deficits, suggesting that impaired learning was related to acquisition of aged immunity and not a nonspecific effect of the transfer procedure. These findings indicate that immune processes may be involved in the etiology of senescence-related neurological/behavioral dysfunctions.

Age-dependent enhancement of diazepam sensitivity is accelerated in New Zealand Black mice

Separate age groups of C57BL/6 and autoimmune New Zealand Black (NZB) mice were compared for diazepam-induced ataxia and barbiturate-induced loss of righting reflex. Between 1 and 3 months of age, both strains showed a similar age-related decrease in ED50 for diazepam-induced ataxia. However, between 3 and 12 months the decrease in ED50 was markedly greater in NZB mice. In contrast, age-related increases in the durations of loss of righting reflex following hexobarbital or barbital were similar in both strains. The results suggest that NZB mice show relatively accelerated age-related increases in sensitivity to benzodiazepine, but not to barbiturates.

Immune manipulations and brain-reactive antibody formation in aging mice

Previous studies have demonstrated an increase in brain-reactive antibodies (BRA) in sera of various mammals as a function of age. The present study attempts to obtain a better understanding of the mode of formation of BRA by using various immunologic manipulations in young and old C57BL/6 mice. The mean BRA levels were significantly higher in older mice than in the young ones. Mixtures of bone marrow cells and spleen cells from old donors were able to adoptively transfer high BRA levels in young irradiated mice and this was not altered by pretreatment of the cells with anti-Thy-1.2 or anti-Ig serum plus complement. Transfer of young cells to old irradiated hosts did not lower the high BRA levels in the hosts. However, when the old hosts were also thymectomized and grafted with neonatal thymuses, BRA levels were significantly lowered. The studies tend to indicate that thymic involution or loss of thymic function in aging plays an important role in BRA formation in sera of aged mice.

Effects of controlled dietary restriction on brain-reactive antibodies in sera of aging mice

Previous studies have demonstrated that underfeeding in both premature and young mature animals may extend the life span as well as preserve the functions of the immune system. The effects of caloric restriction for a period of 12 months on different organs as well as the formation of brain-reactive antibodies in young mature mice (3 months) were tested. These animals showed a significantly lower weight of the total body and various organs including the brain, spleen, adrenals and kidneys. The brain weight/body weight ratio, on the other hand, was significantly higher in these mice. Sera in the dietary animals were mostly negative while those of control animals of the same age and sex had high levels. The present study supports the earlier observations that controlled dietary restriction is able to slow down the age-related deterioration of the immune system. The inhibition of brain-reactive antibody formation in these animals might also be related to a delayed onset of autoimmune disorders.