Immunoregulation in aged humans

Determinants of Serum Immunoglobulin Levels: A Systematic Review and Meta-Analysis

Background

An up-to-date overview of determinants of serum immunoglobulins in adults is pivotal for clinical practice and research, but currently lacking. We therefore performed a systematic review and meta-analysis to identify determinants of serum immunoglobulin levels.

Methods

Embase, Web of Science, Medline, Cochrane, and Google Scholar were searched from inception to July 11th, 2019 for articles reporting on determinants of serum immunoglobulin A, G or M (IgA, IgG or IgM) in adult humans. Random and fixed effect models were applied to obtain pooled mean differences (MDs) and 95% confidence intervals (CIs) for the association of age and sex with serum immunoglobulins.

Results

We retrieved 117 articles reporting on determinants of serum immunoglobulins, of which 28 could be meta-analyzed. Older compared to younger individuals had higher IgA (MD: 0.38; CI: 0.18 - 0.58), but lower IgM levels (MD: -0.40; 95%: -0.66 - -0.14). Men had higher IgA (MD: 0.22; CI: 0.03 - 0.42), but lower IgM levels (MD: -0.21; CI: -0.32 - -0.10) than women. Age and sex did not influence IgG. Caucasian ethnicity was associated with lower IgA, IgG, and IgM. Smoking and corticosteroid use were associated with lower IgG. Positive associations were reported of probiotics with IgG, alcohol with IgA, hypertension with IgA and IgG, and acute psychological stress with IgA, IgG, and IgM.

Conclusions

Older age and male sex are associated with higher IgA, but lower IgM, and urge investigation of age- and sex-specific reference ranges of immunoglobulins. Other identified determinants were ethnicity, diet, lifestyle and cardio-metabolic factors.

Phorbol myristate acetate corrects impaired NK function of old mice

Previous studies indicated that natural killer (NK) activity in mice declined with age. In this report, we investigated the basis for the decreased activity of NK cells in older mice. Our results demonstrated that phorbol myristate acetate (PMA)--an activator of protein kinase C (PKC)--corrects the impaired NK function of older animals. The per cent increase of NK activity post treatment with PMA is 226-261% at effector:target (E:T) ratio = 100:1 compared with control untreated cells. The effect of PMA was shown to be dose dependent. A maximum increase in NK activity was achieved at approximately 10-15 nM PMA. Treatment with PMA does not result in increased binding of NK cells to YAC-1 targets as demonstrated by single-cell assay. In addition, treatment of young NK cells with 1-(5-isoquinolinesulphonyl)-2-methylpiperazine dihydrochloride (H-7), a very potent PKC inhibitor, significantly suppressed NK activity (65% of control). Therefore, we conclude that the age-related decline in murine NK activity may reside in the early signalling events leading to triggering of PKC.

Serology, clinical manifestations and treatment of brucellosis in different age groups

We prospectively studied 339 patients diagnosed of brucellosis over a six year period in order to evaluate the clinical and serological characteristics of brucellosis in the elderly. 319 patients (94.1%) were under 65 years of age (group A), and 20 patients (5.9%) were older than 65 (group B). No patient in group B developed splenomegaly as opposed to 69 (21.6%) in group A (p less than 0.05). The percentage of positive blood cultures (Brucella melitensis isolated in all cases) was 72.1% in group A and 60% in group B. The mean titer of IgM antibodies measured by indirect immunofluorescence test was significantly lower in the elderly patients, with no other differences in serologic response between the two groups. 103 patients (32.2%) in group A and seven patients (35%) in group B developed some complications; spondylitis was more common and severe among group B patients. There was no therapeutic failure or relapse among patients over 65. We conclude that clinical, bacteriological and serological characteristics and the outcome of brucellosis in the elderly are similar to those seen in younger patients.

Influenza vaccination in the elderly: improved antibody response with Imuthiol (Na diethyldithiocarbamate) adjuvant therapy

To improve influenza vaccine efficacy in hospitalized elderly, we compared the evolution of antibody level after vaccination in three patient groups. A sample of apparently primo vaccinated elderly were randomized to receive either Imuthiol (Na diethyldithiocarbamate: group 1) or a placebo (group P). They were compared to patients who had been vaccinated annually for several years (group C). All patients were immunized in the same week. Antibody responses increase within 15 days to reach a plateau in group P and C, while they continue to increase in the Imuthiol treated group, reaching higher antibody levels 30 days after vaccination. This higher antibody rise in group I is essentially due to higher antibody responses in patients with initially low antibody levels and who exhibited at least a four-fold antibody rise. This effect of Imuthiol on influenza antibody responses was observed in spite of a lower nutritional status in this group, a condition that induces lower antibody responses. The higher antibody responses observed in the Imuthiol treated group allow longer protection against influenza.

Alterations in the human immune response to the hepatitis B vaccine among the elderly

The specific binding of hepatitis B (HBs) antigen by lymphocytes from old people immunized with hepatitis B vaccine was explored. For that purpose HBs antigen was combined with fluorescent microspheres, and labeled antigen was allowed to react with lymphocytes from HBs vaccine-responsive or unresponsive people. Lymphocytes from 10 responders and 14 nonresponders were tested for their antigen-binding ability. For controls, lymphocytes were incubated with microspheres bearing human albumin. Lymphocytes from 8 out of 10 responders were able to recognize HBs antigen; for the nonresponders the ratio was 9 out of 14. HBs-binding lymphocytes were B cells but not T lymphocytes. B and T cells from responders and nonresponders were combined and cultivated for 8 days in the presence of HBs antigen, and antibody-producing cells were counted. Neither B cells alone nor B cells plus T cells from nonresponders were able to produce antibody. On the other hand B cells from unresponsive old people produced antibodies when they were cultivated in the presence of HBs antigen and T cells from responsive old people. These data suggest that some elderly individuals who do not produce antibody after in vivo immunization by HBs vaccine do have antibody-producing cells. Instead of a gap in their immune repertoire, these people are suffering from immune dysfunction.

Structural and functional changes of normal aging skin

Solar-induced cutaneous changes are more prevalent and profound in older persons and, thus, are often inappropriately attributed to the aging process, per se. Structural and functional alterations caused by intrinsic aging and independent of environmental insults are now recognized in the skin of elderly individuals. Structurally the aged epidermis likely becomes thinner, the corneocytes become less adherent to one another, and there is flattening of the dermoepidermal interface. The number of melanocytes and Langerhans cells is decreased. The dermis becomes atrophic and it is relatively acellular and avascular. Dermal collagen, elastin, and glycosaminoglycans are altered. The subcutaneous tissue is diminished in some areas, especially the face, shins, hands, and feet, while in others, particularly the abdomen in men and the thighs in women, it is increased. The number of eccrine glands is reduced and both the eccrine and apocrine glands undergo attenuation. Sebaceous glands tend to increase in size but paradoxically their secretory output is lessened. The nail plate is generally thinned, the surface ridged and lusterless, and the lunula decreased in size. There is a progressive reduction in the density of hair follicles per unit area on the face and scalp, independent of male-pattern alopecia. The hair shaft diameter is generally reduced but in some areas, especially the ears, nose, and eyebrows of men and the upper lip and chin in women, it is increased as vellus hairs convert to cosmetically compromising terminal hairs. Functional alterations noted in the skin of elderly persons include a decreased growth rate of the epidermis, hair, and nails, delayed wound healing, reduced dermal clearance of fluids and foreign materials, and compromised vascular responsiveness. Eccrine and apocrine secretions are diminished. The cutaneous immune and inflammatory responses are impaired, particularly cell-mediated immunity. Clinical correlates of these intrinsic aging changes of the skin include alopecia, pallor, xerosis, an increased number of benign and malignant epidermal neoplasms, increased susceptibility to blister formation, predisposition to injury of the dermis and underlying tissues, delayed onset and resolution of blisters and wheals, persistent contact dermatitis, impaired tanning response to ultraviolet light, increased risk for wound infections, prolongation of therapy necessary for onychomycosis, and thermoregulatory disturbances.

Human B-lymphocyte colony responses: suboptimal colony responsiveness in aged humans associated with defective function of B cells and monocytes

The abilities of human B cells from young and aged subjects to form colonies in semisolid cultures stimulated with Staphylococcus protein A were investigated. Approximately three-fourths of aged adults had significantly diminished colony responses compared to young adults. In 55% of these aged adults, the in vitro blocking of monocyte prostaglandin synthesis lead to a 1.5-fold or greater augmentation of the depressed colony responses. Other experiments showed that the improvement with indomethacin could not be explained by the greater sensitivity of aged versus young B-cell colony precursors to prostaglandin suppression. However, indomethacin failed to improve the depressed colony responses of the remaining aged adults. This failure could not be attributed to deficient interleukin 1 production, detectable alterations in accessory cell subsets of monocytes, or the lack of potential colony precursors bearing sIgD/M. Instead, the B cells from these aged subjects demonstrated a substantial decrease in the capping of sIgD/M compared to the B cells of aged subjects which displayed improved colony responses with indomethacin and compared to the B cells from young adults. Thus, these data indicate that the diminished B-cell colony responses of aged humans represent aberrancies within both the B-cell and monocyte lineages which might coexist.

Immune functions in Parkinson's disease lymphocyte subsets, concanavalin A-induced suppressor cell activity and in vitro immunoglobulin production

Immune abnormalities, including the occurrence of autoantibodies against neural structures, diminished numbers of peripheral blood lymphocytes and reduced mitogen responses have been observed in patients with Parkinson's disease. In this study, we found that among the peripheral blood mononuclear cells (PBMNC) of patients with Parkinson's disease, there is a reduced number of cells spontaneously secreting immunoglobulins (Ig). After pokeweed mitogen stimulation, PBMNCs from patients with advanced Parkinson's disease had decreased capacity to elaborate Igs in vitro. In addition, there was evidence suggesting that OKT4+ (helper/inducer) subset may be decreased in Parkinson's disease along with disordered concanavalin A-induced suppressor cell activity. The findings do not primarily suggest an autoimmune pathogenesis of Parkinson's disease. The immune changes now observed partially resemble those seen in normal ageing, though being quantitatively exaggerated in Parkinson's disease. It is suggested that immune abnormalities in Parkinson's disease may result from disordered neural-immune regulation.

Immunosenescence. Clinical and pharmacologic considerations

The effect of aging on the immune response is highly variable. Many individuals appear to maintain adequate immunologic function throughout life, whereas others have severely depressed immunologic responses accounting for disease activity. Both cellular- and humoral-mediated responses may be abnormal in the elderly. Aberrant function of immunoregulatory cells, effector T cells, and antibody-producing B cells contribute to poor immunity in the aged. Immunoenhancement in the elderly by pharmacologic agents appears promising. Several agents have been demonstrated to improve immune responses when administered to aging animals and humans. Although these studies are encouraging, it is not known if enhancement of immune responses in the elderly will be associated with clinical benefits. This issue must still be examined.

Discrepancy in the expression of autoantibodies in healthy aged individuals

Sera from 50 healthy old subjects and from 51 young controls were tested by ELISA assays for a panel of autoantibodies, including IgM RF, anti-DNA, anti-F(ab')2, antithyroglobulin, anti-human albumin, anti-human hemoglobin, anti-secretory component from human IgA, and anti-gliadin. In vitro production of anti-DNA as well as anti-F(ab')2 antibodies were measured after stimulation of PBMC by pokeweed mitogen (PWM) in 12 healthy elderly subjects and 11 young controls. Sera from elderly donors contained threefold higher amounts of IgM RF than young controls (P less than 0.001). On the contrary, the levels of anti-DNA as well as anti-F(ab')2 antibodies were similar in both groups (P less than 0.3 for the two determinations). Anti-DNA and anti-F(ab')2 antibodies were also measured in supernates of PWM-stimulated glass nonadherent PBMC cultures from both old and young healthy donors without finding any significant difference between the two groups. Additional ELISA tests were also performed in both elderly and young control sera to detect antibodies against six other different antigens. No significant difference was found in the percentages of positive sera between the two groups. This discrepancy in production of IgM RF compared to other autoantibodies in healthy elderly subjects does not provide support for a general increase of autoantibodies with aging. The biological significance of an increase in IgM RF with aging remains to be determined.

Ageing and the immune response--a unifying hypothesis?

In this article we review the abnormalities in immune function which have been described in relation to ageing. It is suggested that thymic involution may not be the only underlying cause. Many similar changes can be induced by the endotoxins from the cell walls of Gram-negative bacteria. The colon is a large repository for these organism and bacterial breakdown products are found in portal venous blood. Spillover into the peripheral circulation is prevented by the hepatic Kupffer cells degrading these substances. A waning in Kupffer cell function is well documented in association with ageing and there may be spillover of endotoxins into the peripheral circulation in elderly individuals. It is suggested that such spillover of endotoxins may contribute to some of the immunological changes previously attributed to ageing.

Mechanisms responsible for reduced in vitro immunoglobulin secretion in aged humans

Age-related changes in the processes involved in T cell dependent polyclonal B cell activation in man were studied by comparing immunoglobulin (Ig) produced in autologous T:B (E+:E-) cell cultures of young and old donor pairs with Ig produced in crossover cultures. Each young and old donor was classified as a responder or a non-responder based on Ig levels in autologous pokeweed mitogen-activated T:B cultures. The data indicate that: (1) T suppressor influences are a major determinant of non-response in the young; (2) T cells of nonresponder old donors can support high levels of Ig secretion by young donors' B cells; (3) low response to pokeweed mitogen stimulation in the elderly may reflect either direct refractoriness of B cells to T cell dependent stimulation, heightened B cell sensitivity to suppressor signals, or a combination of the two.

Modulation of T lymphocyte differentiation antigens: influence of aging

In vitro modulation of human T lymphocyte surface differentiation antigens T3, T8, and T4, by their respective monoclonal antibodies, was studied as a function of donor age. Kinetic studies performed on lymphocytes from young adults indicated that modulation is dependent on concentration of antibody used and duration of culture. OKT3 modulates T3 rapidly (maximum at less than 24 hr) and relatively completely (79% at the highest concentration of antibody used). By 48 hr, regeneration of the T3 antigen is apparent. T8 modulation by OKT8 is slower (continued modulation at 48 hr) and less complete than is T3 modulation by OKT3. OKT4 does not modulate the T4 antigen. In elderly individuals modulation of T3 by OKT3 is preserved whereas modulation of T8 by OKT8 is significantly reduced (24 +/- 8% at 48 hr vs 53 +/- 4% for young controls). These observations document further age-related changes in properties of human T suppressor cells.

Studies on the relationship between HLA DR4 and in vitro IgM rheumatoid factor production

The relationship between the presence of the DR4 antigen and other HLA antigens and in vitro production of IgM-rheumatoid factor by lymphocytes from a group of healthy young subjects was examined. Pokeweed and Epstein--Barr virus-stimulated lymphocyte cultures were examined for the production of rheumatoid factor and immunoglobulins. No significant correlation was found between the presence of the DR4 antigen and in vitro production of IgM rheumatoid factor. The presence of the B18 antigen seemed to identify a population of nonresponders when stimulated with PWM.

Cytofluorographic analysis of pokeweed mitogen-stimulated human peripheral blood cells in culture: age-related characteristics

By use of monoclonal antibodies and flow cytometry techniques, peripheral blood mononuclear cells from young (20-30 years) and elderly (70+ years) subjects were analyzed before and after culture with pokeweed mitogen to gain insight into the cellular interactions responsible for the decreased B cell response observed in culture samples from the elderly. Data analysis of surface immunoglobulin-positive cells demonstrated no difference in the percentage of B cells in the elderly, while both plaque-forming cell and intracytoplasmic immunoglobulin assays showed significantly reduced B cell maturation (P = less than 0.01) compared with young controls. The B cell defect was shown to be functional and not a result of failure to proliferate and survive during incubation. Surface marker analysis of T cell subpopulations demonstrated a definite shift (P = less than 0.01) in the helper/suppressor T cell ratio in cultured samples from the elderly group (3.9) compared with young subjects (1.2). In addition to the absolute increase in the helper T cell population, forward-angle light scatter analysis demonstrated that, compared with young controls, a greater portion of the helper T cell population in the elderly subjects had characteristics of activated, blast-sized cells. The data reported in this study suggest that in the elderly group there is a functional immunoregulatory imbalance in the helper T cell subset.

Natural killing and antibody-dependent cytotoxicity by lymphocyte subpopulations in young and aging humans

Natural killer (NK) and antibody-dependent cellular cytotoxicity (ADCC) were examined in the peripheral blood lymphocytes and their major subpopulations from young and aging subjects. Monocyte-depleted unseparated lymphocyte-mediated NK activity (against cells of K-562) and ADCC (against IgG-coated chicken erythrocytes) were comparable between young and aging subjects. Similarly no significant difference was observed in T cell-mediated NK and ADCC and non-T cell-mediated ADCC between young and aging subjects. Non-T cell-mediated NK activity, however, was significantly (P less than 0.025) greater in aging humans compared to that of young subjects. When the data were analyzed according to gender, T cell-mediated ADCC in aging males was significantly (P less than 0.05) greater than that found in young males. No significant difference was observed between T-cell ADCC among young and aging females. T cell-mediated NK was comparable among young and aging males and young and aging females. Non-T cell-mediated NK as well as ADCC activity was significantly (P[ less than 0.025 or less than 0.05) greater in aging males compared to that in young males. Both non-T-cell NK and ADCC were comparable among young and aging females. This study demonstrates an increase in NK and ADCC activity in aging subjects that is primarily shared by males and not by females. No correlation was observed between the proportion of T gamma cells and T-cell NK or ADCC activity.

Decreased in vitro humoral immune responses in aged humans

Induction of antigen-specific and non-specific (polyclonal) humoral immune responses in vitro was investigated in peripheral blood mononuclear cells of aged (65-85 yr) and young (20-30 yr) volunteers. In vitro immunization of lymphocytes with antigen (sheep erythrocytes) was performed in a recently described microculture system, and anti-sheep erythrocyte plaque forming cells were quantitated in a direct hemolytic plaque assay. Immunoglobulin secreting cells, induced polyclonally with pokeweed mitogen, were quantitated in a reverse hemolytic plaque assay. Significant depressions of antigen-specific as well as polyclonal responses were noted in relation to advancing age. Antigen-specific responses were more frequently depressed than polyclonal responses. T cell mitogen concanavalin A (Con A) was used to amplify functions of autologous immunoregulatory T cells. Addition of 10 microgram/ml Con A to lymphocytes of young donors at culture initiation resulted in activation of suppressor cells and abrogated antigen-specific responses. Delayed addition of Con A, on the other hand, enhanced responses, presumably because of activation of helper T cells. Similar manipulations of lymphocyte cultures from aged donors showed failure of Con A to suppress antigen-specific responses in approximately half of the responders. In many nonresponders, responses within normal range were elicited by the delayed addition of Con A to their lymphocyte cultures. Deviations beyond the range of expected responses were noted in 32.5% of the co-cultures between pokeweed mitogen stimulated young and aged cells. Our findings suggest that age-related deficiencies of B cell function are frequently associated with dysfunction of immunoregulatory T cells and are only occasionally due to intrinsic defects of B cells.