White cell function in Down's syndrome

The immune system in Down Syndrome: Autoimmunity and severe infections

Over 200,000 individuals in the United States alone live with Down Syndrome (DS), the most common genetic disorder associated with intellectual disability. DS has a constellation of features across the body, including dysregulation of the immune system. Individuals with DS have both a higher frequency of autoimmunity and more severe infections than the general population, highlighting the importance of understanding the immune system in this population. Individuals with DS present with dysregulation of both the innate and adaptive immune systems. Elevated cytokine levels, increased type I and type II IFN signaling, a shift toward memory phenotypes in T cells, and a decrease in the size of the B-cell compartment are observed in individuals with DS, which contribute to both autoinflammation and severe infections. Herein, we discuss the current knowledge of the immune system in individuals with Down Syndrome as well as ideas of necessary further investigations to decipher the mechanisms by which trisomy 21 leads to immune dysregulation, with the ultimate goal of identifying clinical targets to improve treatment.

Infections and immunodeficiency in Down syndrome

Down syndrome (DS) is the most common genetic disease and presents with cognitive impairment, cardiac and gastrointestinal abnormalities, in addition to other miscellaneous clinical conditions. DS individuals may have a high frequency of infections, usually of the upper respiratory tract, characterized by increased severity and prolonged course of disease, which are partially attributed to defects of the immune system. The abnormalities of the immune system associated with DS include: mild to moderate T and B cell lymphopenia, with marked decrease of naive lymphocytes, impaired mitogen-induced T cell proliferation, reduced specific antibody responses to immunizations and defects of neutrophil chemotaxis. Limited evidence of genetic abnormalities secondary to trisomy of chromosome 21 and affecting the immune system is available, such as the potential consequences of gene over-expression, most significantly SOD1 and RCAN1. Secondary immunodeficiency due to metabolic or nutritional factors in DS, particularly zinc deficiency, has been postulated. Non-immunological factors, including abnormal anatomical structures (e.g. small ear canal, tracheomalacia) and gastro-oesophageal reflux, may play a role in the increased frequency of respiratory tract infections. The molecular mechanisms leading to the immune defects observed in DS individuals and the contribution of these immunological abnormalities to the increased risk of infections require further investigation. Addressing immunological and non-immunological factors involved in the pathogenesis of infectious diseases may reduce the susceptibility to infections in DS subjects.

Impaired neutrophil functions in the pathogenesis of an outbreak of recurrent furunculosis caused by methicillin-resistant Staphylococcus aureus among mentally retarded adults

Staphylococcus aureus is an important cause of skin infections. We recently described an outbreak of recurrent furunculosis involving methicillin-resistant S. aureus among mentally retarded adults. We sought to determine the role of impaired neutrophil functions in its pathogenesis. Blood neutrophil functions were determined during both the outbreak (1997) and a disease-free period (2000). Chemotaxis was measured by migration toward formyl-methionyl-leucyl-phenylalanine (FMLP), specifically and randomly; phagocytosis of opsonized zymosan (OZ) was assessed by microscopy; superoxide production was determined by cytochrome c reduction in unstimulated neutrophils and after stimulation with 50 ng/ml phorbol myristate acetate, 1 mg/ml OZ or 5 x 10(-7)M FMLP. Functions were compared between recurrent furunculosis (n=10) and non-recurrent furunculosis patients (n=13). During 2000, functions were normal among the 23 subjects, except for specific/nonspecific chemotaxis (mean 68%+/-26 and 69%+/-28). During infection, recurrent furunculosis patients had a significantly increased basal superoxide production as compared to disease-free period (10.5+/-4.7 vs. 4.9+/-1.9 nmol O(-)(2)/10(6) cells/min, p=0.003). During the disease-free period, recurrent furunculosis patients had lower basal superoxide production (4.9+/-1.9 vs. 7.7+/-3.5, p=0.067) and impaired specific chemotaxis (57%+/-28 vs. 76%+/-21, p<0.05) as compared to non-recurrent furunculosis patients. Only specific chemotaxis was an independent risk factor for recurrent furunculosis. Mentally retarded adults have impaired chemotaxis, with recurrent furunculosis cases having an even greater impairment. Abnormal specific chemotaxis is an independent risk factor for recurrent furunculosis. Impaired neutrophil functions thus have a role in the pathogenesis of outbreaks of recurrent furunculosis.

Immunology of Down syndrome: a review

Subjects with Down syndrome (DS) have a high mortality due to infections and a high risk of developing malignancies. These observations, together with the demonstration of a frequent occurrence of HBsAg carrier state and of autoantibodies, have prompted investigations of the immune function in DS. Thymic morphological and functional abnormalities have been demonstrated. Peripheral blood mononuclear cells of DS subjects have been shown to include a high number of T lymphocytes with low avidity for sheep erythrocytes and a very high percentage of cells with an NK phenotype. However, NK activity is low in DS. Production of some important cytokines, such as IL-2, is depressed, thus contributing to T-cell derangement. Abnormalities of the B-cell compartment were also demonstrated, with a tendency towards high IgG and low IgM serum levels. Controversial results have been obtained with regard to antigen-specific antibody response. Also phagocytes of DS subjects display some characteristic functional impairments, with low chemotactic ability and reduced production of oxygen radicals. Despite the clearly established and rather detailed evidence of immune derangements, therapeutic trials have been anecdotal and resulted in marginal effects. HBV vaccination is highly advisable in DS because of the high risk of becoming chronic HBV carriers once infected.

Enhanced production of superoxide anion by microglia from trisomy 16 mice

Disruption of normal oxygen radical metabolism in the CNS may contribute to the neuropathological changes associated with Down syndrome (trisomy 21) and its mouse counterpart, the trisomy 16 (Ts16) mouse. One potent source of oxyradicals is the CNS-specific macrophage, the microglial cell. We prepared primary glial cultures from the cerebral cortices of Ts16 and normal littermate mice taken at day 15 of gestation. Microglia were isolated from confluent cultures after 14 days in vitro and assayed for superoxide anion production using a cytochrome C reduction assay. Stimulation by either opsonized zymosan (OPZ) or phorbol myristate acetate (PMA), produced significantly higher levels (2.8-20 fold) of superoxide per mg protein in Ts16 microglial cultures. Resting, i.e. unstimulated secretion, was not significantly different from littermate controls. Astrocyte enriched cultures, stimulated by OPZ, exhibited low levels of superoxide production which was higher in Ts16 mice than normal littermates. Microglial enriched cultures from rat neonatal cerebral cortices were exposed for 24 h to medium from the Ts16 glial cultures. Superoxide production in the Ts16 media treated rat microglia was significantly higher than in those treated with littermate conditioned media.

Periodontal disease in children with Down's syndrome

The occurrence of supra- and subgingival calculus, gingival inflammation, periodontal pockets (greater than or equal to 5 mm) and alveolar bone loss was determined in children (10-19 yr) with Down's syndrome (D-S) and in an aged- and sex-matched control group (n = 39). Of D-S children (n = 71), 39 of the patients (mean age 15.5 yr) cooperated in a clinical and roentgenologic examination. Alveolar bone loss was determined around incisors and first molars on intraoral radiographs when the distance between cementoenamel junction (CEJ) to alveolar crest (AC) exceeded 2.0 mm. Alveolar bone loss was diagnosed in 39% of the D-S children compared to 3% in the control group (P less than 0.001). Of the total number of sites examined on radiographs the distance from CEJ to AC exceeded 2.0 mm in 8% in the D-S group compared to 0.2% in the control group (P less than 0.001). The frequency of sites with alveolar bone loss in D-S children was significantly (P less than 0.001) higher around the mandibular incisors compared to first molars. The study shows that early signs of periodontitis are frequently seen in D-S children as early as 11 yr of age and the lesions are first diagnosed in the mandibular anterior region.

Defective neutrophil chemotaxis in Down's syndrome patients and its relationship to periodontal destruction

The degree of defective neutrophil chemotaxis in patients with Down's syndrome (DS) and its relationship to the severity of periodontal disease were studied. Fourteen patients with DS and 14 healthy controls were examined. Oral hygiene, gingival inflammation, and pocket depths were measured in clinical surveys. Bone loss was evaluated on the oral radiographs. Neutrophil chemotaxis was measured by the agarose plate method and the Boyden chamber method. The chemotactic index of the agarose plate method and the mean numbers of migrated cells of the Boyden chamber method were correlated with statistical significance (rs = 0.066, P less than 0.01). DS patients showed significantly lower chemotaxis than healthy volunteers with both methods. No difference was shown between the two groups in the random migration of the neutrophils. From the oral radiographic analysis, the DS patients exhibited various prevalence of bone loss which was inversely proportional to the chemotactic index and a significant correlation between them was shown (rs = -0.612 P less than 0.05). A significant correlation was also found between the age of the patient and the prevalence of bone loss (rs = 0.591 P less than 0.05). These results indicate that defective neutrophil chemotaxis influences the progression of periodontal disease in DS patients.

Cellular aspects of and effects on the gingiva in children with Down's syndrome during experimental gingivitis

In a previous experimental gingivitis study, it was shown that in children with Down's syndrome (DS), gingival inflammation started earlier, was more extensive and developed faster, than in normal healthy control children. In both groups, the start of the process was accompanied by an acute inflammatory response and an increase of the infiltrated connective tissue area (ICT). The purpose of the present study was to investigate how these facts were reflected at a cytological level. The study was carried out in 8 DS and 8 matched control children. Their ages ranged from 5-10 years. A "normal" healthy gingiva was attained after strict oral hygiene procedures. During a period of 21 days in which oral hygiene was abolished, gingival biopsies were taken on days 0, 7, 14, and 21. In both groups, junctional epithelium (JE) and ICT contained low numbers of polymorphonuclear leucocytes (PMNs). The start of the inflammation (day 7 for the DS and day 14 for the control children) was marked by a significant positive correlation between the numbers of PMNs in the JE and the ICT, and a significant increase of the numbers of PMNs in ICT. In ICT, a concomitant decrease in collagen fibre density was observed. In the control group, the decrease correlated with the numbers of PMNs in ICT, which suggests that this collagen breakdown is caused by PMN products. After the initial decrease, the collagen fibre density remained fairly constant in this group throughout the study. In the DS group, there was a tendency to a further decrease in the ICT3 area, correlated with the numbers of PMNs in ICT.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonspecific and specific immune responses in a child with Down's syndrome and her sibling. A case report

In a child with Down's syndrome (DS) and her sibling, host immune responses were evaluated under experimental gingivitis conditions. The children live in the same environment under identical conditions. In the DS child an earlier and more extensive gingival inflammation than in her sibling had been observed. Investigation of nonspecific host defense mechanisms revealed identical results in both children for the phagocytosis and intracellular killing of Candida albicans by polymorphonuclear leukocytes in crevicular washings (CR-PMNs), in blood (PB-PMNs) and blood monocytes. Furthermore, CR- and PB-PMNs were able to secrete identical amounts of hydrogen peroxide upon stimulation. The chemotactic response of PB-PMNs in the DS child was impaired, however. The results of the studies performed on parameters of specific host defense mechanisms showed low blastogenic responses to phytohemagglutinin (PHA) and pokeweed (PWM) by lymphocytes of the DS child as compared with her sibling. Also a lack of immune regulation leading to prolonged helper/inducer cell activation on a local (gingival) and circulation level and a less pronounced T-cell depression in PB were shown. Together, these differences observed in specific and nonspecific host response mechanisms may be responsible for the earlier and more extensive gingival inflammation found in the DS child.

Periodontal disease in Down's syndrome: a review

Cross-sectional as well as longitudinal studies indicate that the prevalence of periodontal disease in persons with Down's syndrome (DS) under the age of 30 years is extremely high. It is even noted in the deciduous dentition. The progression of the disease is rapid, especially in the younger age groups. Severe periodontal breakdown with horizontal bone loss is often present in the lower anteriors. The large amount of plaque and calculus alone cannot explain the severity of periodontal disease in DS persons. Many contributing factors are reported. Abnormal capillary morphology, disorders in connective tissue and anatomical aspects of teeth are some of those considered to be of influence. Alteration in immunological response may also play a role in the progression of the disease process. Disorders in the polymorphonuclear leucocyte function and monocyte function have been reported in persons with DS. T-cell functioning declines after the first 10 years of life. T-cell lymphocyte counts are low and an immature subset of T-lymphocytes is present. This latter effect occurs especially in institutions where the immunological system is under stress. The altered immune response together with higher calculus scores may explain the difference in severity of periodontal disease between institutionalized DS children and those living at home.

Low superoxide levels in blood phagocytic cells in Down's syndrome

Superoxide anion was measured in polymorphonuclear neutrophils (PMNs) from 10 patients with Down's syndrome (DS) and 10 healthy controls after stimulation with phorobol-myristate-acetate (PMA). The superoxide (O2-) levels were lower in PMNs from nine of 10 DS patients, than in simultaneously tested control cells (p less than 0.01). The findings may in part explain the increased susceptibility of DS patients to infections with certain microorganisms, e.g. S. aureus and C. albicans.

Enzymes of leukocyte oxidative metabolism in Down's syndrome

Enzymes of importance for oxygen dependent leukocyte killing of microorganisms were studied in 14 patients with Down's Syndrome (DS) and 10 controls. As has been reported previously for other cell types, the level of CuZn superoxide dismutase (SOD) was 50% higher in polymorphonuclear leukocytes (PMN) from DS patients than from the controls. The amount of SOD was extremely low in the PMNs from controls, i.e. only about 6% of the levels in other human tissues. The levels of catalase and of the Mn dependent SOD were normal. The myeloperoxidase (MPO) activity of DS PMNs was only 59% of that of the control cells. Previously reported increased levels of CuZnSOD and GSH peroxidase in erythrocytes and CuZnSOD in lymphocytes were confirmed. The increased levels of SOD in DS phagocytes provide a possible partial explanation for previous reports of defective killing of S. aureus in DS. In addition, the MPO deficiency impairs the H2O2-halide-MPO system, which is of particular importance for fungal killing, e.g. of C. albicans, which has also been reported to be deficient in DS. The findings may thus explain some of the mechanisms underlying the increased susceptibility to certain infections in DS.

Down syndrome--a disruption of homeostasis

A major question in human genetics concerns the relationship between the extra chromosome material in the Down syndrome (DS) and its effects. It is suggested here that a generalized disruption of evolved genetic balance in cells of affected individuals leads to decreased developmental and physiological buffering against genetic and environmental forces. Examples of consequences in DS of this model of disruption of homeostasis are presented: i) increased variance for metric traits, ii) amplified instability of developmental pathways, iii) reduced precision of physiological homeostatic controls, and iv) generalized increased morbidity. Evolution has selected for interacting systems. When this evolved balance is disrupted, as in autosomal aneuploidy, the organism is generally disrupted. The model emphasizes the role of environment in producing much of the DS phenotype. Traits less buffered than others in the general population are the ones most disturbed in DS and account for much of the DS phenotype.

Phagocytic function in Down syndrome--II. Bactericidal activity and phagocytosis

Bactericidal capacity was investigated to delineate the impairment of phagocytic function. Fourteen individuals with Down syndrome and fifteen matched institutionalised controls were studied. A non-matched comparison normal group was also evaluated, representing a non-institutionalised young adult population. Neutrophil bactericidal capacity was impaired in institutionalised subjects, the defect being most apparent in Down syndrome. Monocyte bactericidal capacity was identical in institutionalised and non-institutionalised subjects. Humoral functions revealed no differences. Neutrophil phagocytosis was diminished in institutionalised individuals, Down syndrome subjects being the least effective. Monocytes had normal phagocytosis, but opsonisation was defective in both the Down syndrome and matched institutionalised groups. Neutrophils were more efficient at phagocytosis than monocytes. No physiologically significant differences were noted in neutrophil or monocyte intracellular killing.

Phagocytic function in Down syndrome--I. Chemotaxis

Defects in host defences may provide a partial explanation for the increased incidence of infection in individuals with Down syndrome. Neutrophil and monocyte cellular and humoral chemotaxis were evaluated to explore phagocytic function. Fourteen individuals with Down syndrome and fifteen matched institutionalised controls were studied. In addition, a non-matched comparison normal group was investigated, representing a non-institutionalised young adult population. Neutrophil chemotaxis in institutionalised individuals (both Down syndrome and matched controls) was significantly impaired. Monocyte chemotaxis in this group was lower than in comparison normals. Evaluation of humoral components of neutrophil chemotaxis revealed no significant differences between individuals with Down syndrome and those with no known chromosomal abnormality. Down syndrome subjects had diminished humoral monocyte chemotactic responses compared with institutionalised controls and normal subjects.

Zinc and immune function in Down's syndrome

Low levels of zinc in serum and high in blood clots were found in 12 patients with Down's syndrome (DS). They also had an immune deficiency characterized by depressed neutrophil chemotaxis, skin hypersensitivity and lymphocyte responsiveness to PHA in vitro. The patients received zinc sulphate, corresponding to 135 mg Zn++ daily. After treatment for 2 months' serum zinc levels had increased, neutrophil chemotactic responsiveness was normal in 11 of the 12 patients and there were improved lymphocyte responses to high doses of PHA in vitro. Delayed skin reactivity to DNCB was also improved in 10 of 11 patients after zinc therapy. Zinc deficiency may in part explain the increased susceptibility to infection in DS.