D. Quaglino

The immune system in the elderly : I. Specific humoral immunity

Profound and complex changes in the immune response occur during the aging process. Immunosenescence is reflected by a sum of disregulations of the immune system and its interaction with other systems. Many of the changes would appear to implicate age-related deficiencies of the immune responses. The term immunosenescence designates therefore a sort of deterioration of the immune function which is believed to manifest itself in the increased susceptibility to cancer, autoimmune disease, and infectious disease. Evidence has been accumulating from several studies which suggest an association between immune function and individual longevity. However, there are observations, especially in very old healthy people, that several immune functions are unexpectedly well preserved and substantially comparable to those observed in young subjects. These findings raise the question of whether the alterations that can be observed in the immune parameters of the elderly are a cause or a result of underlying disease processes. Moreover, studies on centenarians revealed a remodeling of the immune system rather than a deterioration, suggesting that the changes observed during immunosenescence do not correspond to immunodeficiency. The underlying mechanisms of these events are however still unclear. The purpose of the present review is to assess the status of research on the immunobiology of aging. In this first section, we focus attention on the B cell biology of aging. In clinical practice, the changes in humoral immune responsiveness and antibody-mediated defense mechanisms could greatly influence the incidence and outcome of bacterial infections and autoimmune diseases as well as the response to vaccines.Profound and complex changes in the immune response occur during the aging process. Immunosenescence is reflected by a sum of disregulations of the immune system and its interaction with other systems. Many of the changes would appear to implicate age-related deficiencies of the immune responses. The term immunosenescence designates therefore a sort of deterioration of the immune function which is believed to manifest itself in the increased susceptibility to cancer, autoimmune disease, and infectious disease. Evidence has been accumulating from several studies which suggest an association between immune function and individual longevity. However, there are observations, expecially in very old healthy people, that several immune functions are unexpectedly well preserved and substantially comparable to those observed in young subjects. These findings raise the question of whether the alterations that can be observed in the immune parameters of the elderly are a cause or a result of underlying disease processes. Moreover, studies on centenarians revealed a remodeling of the immune system rather than a deterioration, suggesting that the changes observed during immunosenescence do not correspond to immunodeficiency. The underlying mechanisms of these events are however still unclear. The purpose of the present review is to assess the status of research on the immunobiology of aging. In this first section, we focus attention on the B cell biology of aging. In clinical practice, the changes in humoral immune responsiveness and antibody-mediated defense mechanisms could greatly influence the incidence and outcome of bacterial infections and autoimmune diseases as well as the response to vaccines.

Immunological changes in the elderly

Immunosenescence is a complex remodelling of the immune system which may contribute significantly to morbidity and mortality in the elderly. Much evidence suggests an association between immune function and longevity. It was advanced that individuals who have survived in good health to the maximum life span are equipped with optimal cell defense mechanisms. Despite the great number of studies on the immune system in the elderly, little is known of the biological basis of immunosenescence in humans. This is partly due to the contrasting results often obtained by the various investigators. One source of discrepancy is that diseases are frequent in aging, and the alterations observed in the immune parameters of the elderly could be a cause or alternatively a consequence of the underlying pathological processes. Undoubtedly some diseases to which aged people are particularly susceptible, such as infectious, autoimmune and neoplastic pathologies, include dysregulation of several immune functions in their pathogenesis. On the other hand, recent studies in healthy centenarians suggest that the immunological changes observed during aging are consistent with a reshaping, rather than a generalized deterioration, of the main immune functions. Considering that the number of old people is dramatically increasing, and that geriatric pathology is becoming an important aspect of clinical practice, it seems particularly interesting to review the peculiar findings in the immune system of the elderly so as to better understand their susceptibility to certain diseases, and the links between health and longevity.

Immunophenotypical Changes of T Lymphocytes in the Elderly

Background: Substantial changes in both representation and function of T lymphocyte subsets have been reported with advancing age. However, till now, no systematic studies focused on age-dependent changes in the expression intensity of the major T lymphocyte surface receptors. Objective: The present study was undertaken in order to establish age-related differences in lymphocyte subpopulations by simultaneously measuring three surface antigens in young and elderly people. Method: Peripheral blood T cell subsets from 20 healthy elderly individuals and 15 healthy young adult donors were examined by means of a quantitative three-color flow cytometry method. Results: Activated (HLA-DR+) and memory (CD45RO+) T cells, CD3+CD7– T lymphocytes, and cells expressing natural killer (NK) markers (CD3–CD56+ NK cells and CD3+CD56+ T lymphocytes) were expanded, whereas T lymphocytes expressing the adhesion molecule CD62L were lower in elderly compared with young donors. In addition to alterations in the percentages of T cell subsets during senescence, several changes in the intensity expression of T cell antigens were also detected. CD3 antigen expression was downregulated on total T lymphocytes as well as on the memory T cell subset, while CD56+ T cells exhibited increased CD3 levels. Moreover, CD2 expression, unchanged on NK cells, was upregulated on T lymphocytes from elderly subjects. CD3+CD7– T cells exhibited increased expression of CD8 antigen, while the intensity expression of HLA-DR on activated T cells and CD7 on both T and NK lymphocytes was decreased. T cells from elderly subjects also exhibited higher expression of CD50 and CD62L adhesion molecules as compared with young ones. Conclusion: These T cell antigen expression modulations during senescence, in addition to the alteration in the frequency of the various T lymphocyte subsets, could contribute to the complex remodeling of the immune function characteristic of the elderly.

Cell Proliferation and Apoptosis in the Immune System in the Elderly

Loss of the cell proliferative capability and involution of tissues and organs are among the most important phenomena that characterize the aging process. Some of the aged-linked immune dysfunctions could be partly due to a dysregulation of apoptotic processes and to a lower responsiveness of aged lymphoid cells to activation and proliferation signals. The main changes in proliferative activity and cell death during aging and their impact on the process of immunosenescence are discussed. In fact, a very important function that has been suggested to deteriorate with age and to play a major role in the aging process is the capability of cells from aged subjects to respond to mitogenic stimuli and, consequently, to undergo cell proliferation. However, the cellular activation processes are very complex and the proliferative responses can follow different interconnected signal transduction pathways, and only some of them appear to be modified during age. Moreover, cell growth, immunosenescence, and longevity are strictly interconnected and deeply related to programmed cell death or apoptosis. The cellular equilibrium between cell survival and proliferation, on the one hand, and programmed cell death, on the other hand, seems to be unbalanced with advancing age, although in each type of immune cell it could be differentially modulated, resulting in a variety of clincopathological consequences. Thus, cell proliferation and cell death are two physiologically active phenomena closely linked and regulated and a failure of these mechanisms determines profound dysregulations of cell homeostasis with major consequences in immune functioning and the onset of autoimmune diseases and cancer, whose incidence appears to be increased in the elderly.

Cytobiological and Clinical Aspects of Tissue Mast Cell Leukaemia

Summary. The authors describe the results of a series of cytochemical, autoradiographic, cytophotometric and immunological investigations carried out in a case of tissue mast cell leukaemia. Leukaemic mast cells showed certain distinctive cytochemical features, amongst which an intense periodic acid‐Schiff (PAS) reaction, sensitive to amylase digestion, strong naphthol AS‐D chloroacetate esterase (NASDCE), intense lactate dehydrogenase (LD) activity. Proliferative activity, determined autoradiographically with 3H‐dT, was considerably low and was mainly confined to the larger cells. Also uridine and leucine incorporation were markedly reduced. Microdensitometry disclosed that the mast cell population was mainly arrested in the G1 phase. Because of previous attempts to destroy selectively neoplastic tissue mast cells with sheep antihuman IgE serum, a search for surface bound IgE was carried out, but gave a negative result. Possible therapeutic approaches are considered in the light of previous clinical experience and on the basis of the results of the kinetic and metabolic studies.

Adhesion molecules on peripheral blood lymphocyte subpopulations in the elderly.

Adhesion molecules, such as CD49d, CD50 and CD62L, have important roles in many adhesive interactions involving cells of the immune system. Since it has been shown that many immunological alterations are present in aged subjects, we studied, by means of triple colour whole blood immunostaining and multiparametric flow cytometry, the expression and intensity level (MFI) of these molecules on peripheral blood lymphocyte subpopulations from 23 healthy elderly subjects and 13 young controls. In the elderly a decrease in total peripheral blood lymphocytes bearing CD62L antigen was observed (39 +/- 13% vs 63 +/- 6% and 745 +/- 312/mm3 vs 1,393 +/- 407/mm3; p<0.001), whereas the numbers of lymphocytes expressing CD49d and CD50 antigens were comparable in aged and young subjects. In addition, CD50 and CD62L MFI values on total peripheral blood lymphocytes were higher in elderly than in young subjects (5.23 +/- 1.03 vs 4.18 +/- 0.44, p = 0.001 and 2.60 +/- 0.35 vs 2.21 +/- 0.40, p = 0.005 respectively) while the intensity expression of CD49d was unchanged. The percentages and absolute numbers of T and B lymphocytes expressing CD62L were decreased in elderly compared to young subjects (CD62L+CD3+: 43 +/- 15% vs 66 +/- 9% and 581 +/- 257/mm3 vs 1,028 +/- 418/mm3, p<0.001; CD62L+CD19+: 78 +/- 12% vs 90 +/- 4%, p < 0.005 and 103 +/- 64/mm3 vs 207 +/- 98, p < 0.001). A decrease in the proportion of CD62L bearing NK cells was also observed in the elderly (25 +/- 14% vs 46 +/- 24%, p<0.005), although their absolute number was unchanged. No significant differences were detected in the proportion of T, B and NK lymphocytes expressing CD49d and CD50 antigens and only the absolute numbers of B cells expressing these adhesion molecules were lower in elderly (CD49d+CD19+: 121 +/- 71/mm3 and CD50+CD19+: 107 +/- 73/mm3) compared to young donors (CD49d+CD19+: 248 +/- 112/mm3 and CD50+CD19+: 235 +/- 120/mm3, p < 0.001). Moreover, the intensity of adhesion molecule expression was differentially modulated in the elderly depending on the specific lymphocyte cell population considered. The densities of CD49d, CD50 and CD62L antigens on B and NK lymphocytes from the two age groups were not different; on the contrary, T lymphocytes from elderly donors exhibited increased CD49d (1.69 +/- 0.09 vs 1.62 +/- 0.07, p < 0.05), CD50 (4.98 +/- 1.16 vs 3.77 +/- 0.46, p < 0.001) and CD62L (2.26 +/- 0.38 vs 1.99 +/- 0.37, p < 0.05) MFI values compared to young donors.

EMPERIPOLESIS OF GRANULOCYTES WITHIN MEGAKARYOCYTES

have also been described (Pandolti et al , 1982: Baldini et 111, 1985). CD4 + prolifcrations in general have a inore aggressive course than the C I M + large grariular lymphocyte proliferations that are dcscribed (Raldini et 01. 1985: Witzig et (41, 1984). The striking feature of the mature CD8+ proliferations is the marked cytopenias that occur. The CD4 proliferation described by VanSlyck et al is indeed unusual because of the marked haemopoietic suppression and low grade clinical course and we have not as yet seen a similar case. Although the expression of (2114 and CD8 antigen broadly defines functional populations there is increasing evidence that each population contains many subsets with different and often overlapping functional properties. Fuller investigation of these unusual cases may help in the recognition of their normal functional counterparts. Deport men t oJ Haemntology . London Hospital Medical College. Turner Street, London E l 1 H H A. C. NEWLAND

Activated Naive and Memory CD4+ and CD8+ Subsets in Different Stages of HIV Infection

The aim of this study was to evaluate the changes and the correlations between the main lymphoid phenotypes indicative of activation and/or functional states during the course of HIV infection. Immunophenotype studies by flow cytometry were performed on blood samples from 59 HIV-1-positive patients, divided into four stages, and 18 seronegative healthy controls, to determine the expression of HLA-DR, CD29 and CD45RA on CD4+ and CD8+ lymphocytes. HLA-DR expression was elevated on the total lymphocyte population and in both the main T subsets. Its presence on CD4+ lymphocytes probably has a different significance in the first phase of infection when it is indicative of reactive activation, in contrast to the more advanced stages of disease when it favors the spread of HIV infection among this cellular subset. The increasing state of immune activation is also confirmed by a proportional decrease in the expression of CD45RA, substantial stability of CD29 and an increase in double-negative CD4+ cells as the infection proceeds. Also CD8+HLA-DR+ lymphocytes increase during the course of disease. The parallel increase of the CD8+CD45RA+ subset in asymptomatic patients suggests the presence in this phase of infection of peripheral blood immature and activated CD8+ cells. Similarly to CD4+, the CD29 subset of CD8+ lymphocytes remains unchanged compared to controls during disease progression. In both CD4+ and CD8+ subsets we observed the increase of a double-negative sub-population of uncertain significance. HLA-DR, the memory marker CD29 and the naive marker CD45RA seem to be the more promising and helpful indicators for a better staging of disease and may provide information that accurately correlates with progression of infection. The peculiar trend of the described phenotypic alterations could represent changes in the immune response to HIV during disease progression and facilitate the definition of specific immune patterns in different stages of HIV infection.

The effect of age on hemopoiesis

Although several workers have described numerous changes affecting the hemopoietic system during senescence, the existence of univocal “hematological disease” closely related to the elderly is controversial. Many of the hematological changes described, such as sideropenic or megaloblastic anemia, are frequently the consequence of the different pathological conditions which often affect elderly patients. This review will consider the most important alterations of hemopoiesis and coagulation in the elderly, the causes capable of influencing hematological changes in old people, and their pathogenesis. Some of the major diagnostic problems encountered in the management of elderly subjects with hematological changes are also addressed. In the presence of an elderly patient with hematological alterations, it is necessary to follow a precise diagnostic schedule, which should first of all exclude the presence of a primary hematological disorder, and consider the different extrahematological conditions which frequently occur in elderly subjects (malignancies, malnutrition, chronic infections from immunological abnormalities, hormonal changes, deficiencies of various organs and systems etc.) and are responsible for many different hematological changes. These must be tackled rationally so that treatment may not only be symptomatic, but may also directly intervene on the cause of the disorder.

Dipeptidyl Amino Peptidase IV Cytochemistry in Circulating Lymphocytes from HIV-I-Seropositive Subjects

In order to assess whether changes in the relative proportions of cells pertaining to different T-lymphocyte subsets correlate with dipeptidyl amino peptidase IV (DAP IV) activity, the enzyme was cytochemically investigated in circulating lymphocytes from 20 HIV-I-seropositive drug addicts. Although on the average, a significant reduction of lymphocyte DAP IV activity was found in comparison with healthy control subjects, wide variations between individual cases were observed, and no obvious relationship emerged between DAP IV staining on one hand, immunocytological findings and Walter Reed staging on the other. Therefore, in view of the preliminary results reported, the variations of lymphocyte DAP IV activity in the course of HIV I infection seem to deserve further investigation, in order to clarify both the biological significance of this reaction and its possible clinical relevance.