Rajabather Krishnaraj

Cytokine sensitivity of human NK cells during immunosenescence. 2. IL2-induced Interferon gamma secretion

A majority of natural killer (NK) cells constitutively express intermediate affinity IL2 receptors made of beta gamma chains and respond by way of enhanced cytokine secretion. However, alterations in cytokine sensitivity of purified NK cells with respect to cytokine secretion during immunosenescence have not been examined before. In view of the major immunomodulatory role of IL2 and the anti-tumor effects of interferon gamma (IFN-gamma), we have investigated the recombinant human IL2-induced NK cell secretion of IFN-gamma in vitro. After an 18-h activation period, the secretion of IFN-gamma by the peripheral blood NK cells from the elderly was severely impaired at 80 U/ml of IL2 and above. At an optimal dose of IL2 (960 U/ml). NK cells from young and elderly showed a mean 11- and 3-fold increase in secretion, respectively. Under similar conditions, purified T cells did not respond to IL2. However, the sensitivity of NK cells to the same inductive ligand, IL2, towards a different function i.e., cytotoxic activity, was not significantly impaired in the aged. It is possible that the cytokine secretory deficiency of senescent NK cells might be an additional mechanism which could favor the establishment of tumors and viral infections in the elderly. However, as discussed here, our findings do offer alternate explanations and a potential target for experimental immunotherapy.

Low Natural Killer Cell Function in Disseminated Aspergillosis

We investigated whether immune deficiency was associated with a fatal case of invasive cerebral aspergillosis due to Aspergillus fumigatus infection. The lymphocyte proliferative capacity to T- and B-cell mitogens was comparable to that of healthy controls. However, the natural killer (NK) cell activity of the patient was 2-6-fold lower than the activity expressed by a paired control and age-sex matched healthy controls (n = 20). No specific abnormalities were evident in the capacity to transduce either proliferative signals or cytokine (interleukin 2) secretory capacity of in vitro activated lymphocytes from the patient. The specific reduction in NK cell activity might either indicate that she was a low NK responder, or that the low NK cell activity was primarily or secondarily associated with the fungal infection caused by Aspergillus fumigatus in humans.

Negative modulation of human NK cell activity by purinoceptors: 2. Age-associated, gender-specific partial loss of sensitivity to ATP

Aging is known to modulate the affinity and sensitivity of receptors for hormones and regulatory molecules. We have shown previously that exogenous adenosine triphosphate (ATP), perhaps acting as a purinoceptor agonist, can down-regulate the cell-mediated anti-tumor natural cytotoxic activity of human peripheral blood natural killer (NK) cells. We have extended these studies to investigate whether this effect is modulated during immunosenescence, and if so, whether it is gender-restricted or NK subset-associated. While the inhibitory effect is demonstrable in most individuals, there is a gender-restricted, age-associated transition in the sensitivity of NK cell activity to inhibition by ATP at 2.5 x 10(-5) to 80 x 10(-5) M in vitro. Data from both suboptimal (100 microM) and optimal (800 microM) inhibitory doses of ATP support this conclusion. The ID20ATP were 10.2 x 10(-5) and 17.8 x 10(-5) M for the young (less than 40 years) and elderly (greater than 70 years) females, respectively (P = 0.02). The frequency distribution curve of ATP sensitivity shifts to the left in the elderly, i.e., the sensitivity to be inhibited at 50% or more by ATP was expressed by one-half of young and one-fifth of elderly female donors. Linear regression analysis suggests an inverse relationship between percentage CD57+ and percentage CD16+57+ (but not percentage CD16+) NK subsets and sensitivity to down-regulation by ATP. The mean percentage of the above NK cell phenotypes among lymphocytes from young and old female donors differ significantly (less than 0.0001). The data suggest that the presence of CD57 antigen-positive cells may render NK cells relatively more resistant to the action of purinoceptor agonists such as ATP. Thus in females, immunosenescence results in a diminished ability of NK cells to transduce those signals that may normally mediate ATP-induced suppression of NK cytolytic activity. Such a diminished ability may be an immunobiological advantage to aging NK cells since they can be kept at a higher steady-state level of (anti-tumor cytotoxic) activity through a protection from negative modulators. These findings have an implication on the lower rate of mortality due to cancer seen in older women compared to that in older men. It is suggested that the ATP-NK cell interaction through the P2 purinoceptor may serve as a potentially useful model to study immunosenescence, ontogenic, or gender-specific changes in NK cells at the cell surface level.

Black cohosh (Actaea racemosa) for the mitigation of menopausal symptoms: recent developments in clinical safety and efficacy

The purpose of this article is to assess recent data supporting the safety and efficacy of black cohosh products for the mitigation of menopause-related symptoms. Searches of the published literature in Napralert, Cochrane Library and PubMed databases were performed from 2003 to 2006. Information from drug regulatory agencies from five different countries was obtained to evaluate safety. While there are a few contradictory studies, the majority of the clinical trials indicate that extracts of black cohosh (Actaea racemosa L.) improve menopause-related symptoms. However, to date, at least 50 cases of possible hepatotoxicity have been reported. Although previous safety reviews suggest that black cohosh is well tolerated, the increasing numbers of these case reports indicates that further preclinical toxicological evaluations of black cohosh are urgently needed. At this time, it appears prudent to advise menopausal women with underlying liver disease, autoimmune diseases or those taking medications that may impact liver function not to use products containing black cohosh.

Immunomodulation by 9-amino-1,2,3,4-tetrahydroacridine (THA): 1. Down-regulation of natural cell-mediated cytotoxicity in vitro

THA (Tacrine), a drug used in the experimental therapy of dementia of Alzheimers disease type, and whose biochemical site of action is believed to be the neural cholinesterase, is shown, for the first time, to be an immunosuppressant in vitro on normal human peripheral blood lymphocytes in microgram quantities. THA down-regulates non-MHC restricted natural killer (NK) cell activity without affecting the general viability of cells. This down-regulation can be demonstrated at all effector and target (K562) concentrations, in purified resting NK cells as well as in lymphokine (interleukin 2) activated killer cells in 3- or 16-h NK assays and in all the blood samples tested. Kinetic analysis shows that the Vmax (maximal cytotoxic potential) and Km of NK cell-mediated cytolysis are also attenuated. Single cell assays using agarose matrix reveal that THA moderately interferes with tumor target binding/recognition events and strongly abrogates the delivery of lethal hit, thus lowering the frequency of active killer cells among THA-treated lymphocytes. THA down-regulates NK cells upon direct interaction and does not require the help of non-NK cells. The THA sensitive site(s) on NK cells does not appear to be perturbed significantly either by their proliferative status or by membrane modulations that may be normally induced by interleukin 2. The in vitro immunomodulatory pharmacological properties of THA reveal that the biological site of action of THA extends to non-neural cells also. Such non-neural models may be helpful in exploring the pathophysiological neuroimmunomodulatory properties of THA at cellular and molecular levels.

Immunosenescence and Human NK Cells

Of the three major cellular components of the lymphoid system, both T- and B-cell systems have been fairly well investigated with special reference to senescence-related changes in man and experimental animals (Makinodan and Kay, 1976; Weksler, 1982). It is widely believed that a general decline in immune competence (as seen in aging) is related to the high incidence of cancer. Despite the fact that the natural killer (NK) cells are known to play a role in immunosurveillance against malignancy and viral infection, and the regulation of hematopoiesis (Herberman and Holden, 1978, Trinchieri and Perussia, 1984), there are no strong data linking a vigorous NK cell system with healthy cancer-free survival to old age in humans. Peripheral blood NK activity is known to increase gradually from birth to adulthood (Herberman and Holden, 1978). However, the dynamics of the NK system from adulthood to old age (aging effect?) have not been studied systematically in healthy volunteers. Previously available literature showed equivocal results or had some methodological problems. In trying to investigate the quantitative and qualitative aspects of the immunosenescent changes in the NK cell system, we have asked three major questions: 1. Is it possible to demonstrate experimentally, an age-associated, but not necessarily an age-dependent change (see Chapter 11 this volume), in human peripheral blood NK activity by a multitechnique approach? The resulting pattern of NK cell dynamics should be qualitatively consistent with different traditional as well as unconventional techniques and experimental conditions used to quantitate the NK activity. 2. Would such a functional change in NK activity—whether positive or negative— have a cellular basis? If so, would those phenotypic alterations be unique to the aging process? 3. Are there parallel immunosenescent changes in the non-null cel (T and B) systems? Do the NK cells have an immunoregulatory influence on the non-NK cell immune systems of an aging individual?