Increased frequency of proangiogenic tunica intima endothelial kinase 2 (Tie2) expressing monocytes in individuals with type 2 diabetes mellitus.

BACKGROUND: Individuals with type 2 diabetes mellitus (T2DM) have an increased risk for developing macrovascular disease (MVD) manifested by atherosclerosis. Phenotypically and functionally different monocyte subsets (classical; CD14++CD16-, non-classical; CD14+CD16++, and intermediate; CD14++CD16+) including pro-angiogenic monocytes expressing Tie2 (TEMs) can be identified. Here we investigated monocyte heterogeneity and its association with T2DM and MVD. METHODS: Individuals with (N = 51) and without (N = 56) T2DM were recruited and allocated to "non-MVD" or "with MVD" (i.e., peripheral or coronary artery disease) subgroups. Blood monocyte subsets were quantified based on CD14, CD16 and Tie2 expression levels. Plasma levels of Tie2-ligands angiopoietin-1 and angiopoietin-2 were determined using ELISA. Carotid endarterectomy samples from individuals with (N = 24) and without (N = 22) T2DM were stained for intraplaque CD68+ macrophages (inflammation) and CD34+ (angiogenesis), as plaque vulnerability markers. RESULTS: Monocyte counts were similar between individuals with T2DM and healthy controls (non-diabetic, non-MVD). Non-classical monocytes were reduced (p < 0.05) in T2DM, whereas the percentage of TEMs within the intermediate subset was increased (p < 0.05). T2DM was associated with increased angiopoietin-1 (p < 0.05) and angiopoietin-2 (p = 0.0001) levels. Angiopoietin-2 levels were higher in T2DM individuals with MVD compared with non-MVD (p < 0.01). Endarterectomized plaques showed no differences in macrophage influx and microvessel number between individuals with and without T2DM. CONCLUSIONS: Monocyte subset distribution is altered in T2DM with reduced non-classical monocytes and increased TEM percentage in the intermediate monocyte subset. Increased angiopoietin-2 levels together with increased frequency of TEMs might promote plaque vulnerability in T2DM which could however not be confirmed at tissue level in advanced atherosclerotic lesions.

Airway eosinophilia in remission and progression of asthma: accumulation with a fast decline of FEV(1).

BACKGROUND: As it is unknown whether complete asthma remission or progression of asthma is associated with airway inflammation and remodeling, we assessed these characteristics in bronchial biopsies of relevant subsets of asthma patients. METHODS: Sputum and bronchial biopsies were obtained from asthma patients in remission (PC(20) histamine> 32 mg/ml, PC(20) AMP> 320 mg/ml) and from those with either a slow FEV(1) decline (< 30 ml/year) or fast decline (> 30 ml/year). Inflammatory cells and mediators were determined in sputum, inflammatory cells and aspects of airway remodeling in bronchial biopsies. RESULTS: Asthmatics in remission and asthma patients with a slow FEV(1) decline had a similar extent of airway inflammation and remodeling in sputum and bronchial biopsies. Asthma patients with a fast FEV(1) decline had high sputum eosinophil numbers. Moreover, FEV(1) decline (ml/year) correlated with sputum eosinophil numbers (Rs=0.51, p=0.003) and ECP levels (Rs=0.57, p=0.001). Airway remodeling, i.e. basement membrane thickness, correlated with sputum eosinophils (Rs=0.69, p<0.001), sputum ECP (Rs=0.46, p=0.018) and airway wall eosinophil numbers (Rs=0.49, p=0.002). CONCLUSIONS: Asthma, even when in remission, is accompanied by airway inflammation and remodeling. Data suggest that eosinophils are important in a subset of asthma patients by association to accelerated FEV(1) decline and change of basement membrane thickness.

Complement dependency of splenic localization of pneumococcal polysaccharide and conjugate vaccines.

The immune response to polysaccharides is initiated when polysaccharides bind complement factor C3d, and these polysaccharide-C3d complexes subsequently localize on splenic marginal zone B cells strongly expressing CD21 (complement receptor 2). Infants and children under the age of 2 years have low or absent expression of CD21 on their marginal zone B cells, and consequently do not adequately respond to polysaccharides. In contrast, polysaccharide-protein conjugate vaccines are able to induce antibodies at this young age. Conjugate vaccines apparently overcome the necessity for CD21-C3d interaction for an antipolysaccharide immune response. We demonstrate in a rat model that localization of pneumococcal polysaccharides on splenic marginal zone B cells indeed is complement dependent. We also show that pneumococcal conjugates do not specifically localize on splenic marginal zone B cells and that splenic localization of polysaccharide conjugates is independent of the presence of complement. Thus, the induction of antipolysaccharide antibodies by conjugate vaccines apparently can occur independently of CD21-C3d interaction. These basic findings may explain the effectiveness of conjugated vaccines in young children and may open the way for their application in other patient groups.

Effects of multidose combination chemotherapy on the humoral immune system.

Patients receiving multidose combination chemotherapy are at risk for severe, life-threatening infections, caused by among others encapsulated bacteria like Streptococcus pneumoniae. The splenic marginal zone is essential in the initiation of immune responses to S. pneumoniae. We analyzed effects of multidose combination chemotherapy on B-cell subpopulations. Immune response capacity was evaluated by using Pneumovax (PPS) or Tetavax (TT) as antigenic challenge. Three days after finishing therapy, all B-cell subpopulations in bone marrow and spleen were severely reduced, including the mature marginal zone B-cell population. When analyzing the anti-PPS immune response capacity at 3 days after finishing therapy, we found that the IgM antibody levels did not differ significantly from control immunized rats. The IgG antibody levels were significantly lower compared to control immunized rats but still significantly higher compared to unimmunized rats. The depletion of marginal zone B cells by multidose combination chemotherapy most likely contributes to the prolonged period that patients are at risk for developing severe infections after chemotherapy, despite the capacity to generate sufficient antibody levels. It is conceivable that the local (temporary) loss of immunological memory, together with the supposed inability to generate a humoral response in a short time frame, plays an important role in this vulnerability.

After chemotherapy, functional humoral response capacity is restored before complete restoration of lymphoid compartments.

Chemotherapy has, besides the beneficial effects, several adverse effects. Suppression of the immune system is one of the most important problems. Infections caused by encapsulated bacteria like Streptococcus pneumoniae are responsible for a major part of infectious problems during and after treatment. The splenic marginal zone is essential in the initiation of an immune response to encapsulated bacteria. In this study, we analysed the effects of three different cytostatic agents on humoral immune responses. We found a reduced, but detectable immune response capacity at two days after treatment although the marginal zone B cell population is severely reduced at this time point. Twenty-four days after cessation of treatment, the immune response capacity was largely restored although lymphoid compartments were still not completely restored at that time point. Apparently, the presence of only few marginal zone B cells is sufficient to evoke a rise in antibody titres and although antibody titre increases are low, even small rises are most likely clinically relevant.

Pneumococcal conjugate vaccines overcome splenic dependency of antibody response to pneumococcal polysaccharides.

Protection against infections with Streptococcus pneumoniae depends on the presence of antibodies against capsular polysaccharides that facilitate phagocytosis. Asplenic patients are at increased risk for pneumococcal infections, since both phagocytosis and the initiation of the antibody response to polysaccharides take place in the spleen. Therefore, vaccination with pneumococcal polysaccharide vaccines is recommended prior to splenectomy, which, as in the case of trauma, is not always feasible. We show that in rats, vaccination with a pneumococcal conjugate vaccine can induce good antibody responses even after splenectomy, particularly after a second dose. The spleen remains necessary for a fast, primary response to (blood-borne) polysaccharides, even when they are presented in a conjugated form. Coadministration of a conjugate vaccine with additional nonconjugated polysaccharides of other serotypes did not improve the response to the nonconjugated polysaccharides. We conclude that pneumococcal conjugate vaccines can be of value in protecting asplenic or hyposplenic patients against pneumococcal infections.

Slow recovery of follicular B cells and marginal zone B cells after chemotherapy: implications for humoral immunity.

Although most chemotherapeutic agents are known to cause primarily reduction or suppression of immune responses, surprisingly little is known about the influence of cytostatic agents on lymphoid tissue compartments such as the splenic marginal zone. The marginal zone plays an important role in the defence against encapsulated bacteria, which are potential candidates for postchemotherapeutic infections. We studied the effect of three different cytostatic agents (cisplatin, methotrexate, and cyclophosphamide) on B cell subpopulations in a rat model. Rats received a single dose of a single cytostatic agent and were sacrificed at different time points after treatment. Bone marrow, blood, mesenteric lymph nodes and spleens were analysed by flow-cytometry and immunohistochemistry. All three cytostatic agents showed severe bone marrow depression. CP and MTX showed only mild reduction of cell populations in the spleen. CyPh showed a severe reduction of recirculating follicular B (RF-B) cells and marginal zone B (MZ-B) cells. At day 24 most populations were already recovered, but RF-B cells and MZ-B cells were still reduced. The reduction of the marginal zone and late recovery may imply that, beside the overall increased infection risk due to neutropenia, patients treated with chemotherapy are at risk for developing infections from encapsulated bacteria for a considerable period of time after treatment, extending beyond the period of bone marrow depression.

CD27 expression in the human splenic marginal zone: the infant marginal zone is populated by naive B cells.

The splenic marginal zone of adult humans contains B cells, of which most express CD27, an antigen only recently identified as a marker for somatically mutated memory B cells. We investigated whether and to which extent the developing marginal zone in infants and children is populated by either memory (CD27+) or naive (CD27-) B cells. Frozen sections of 32 spleens of infants and children ranging in age from 6 days to 15 years and 6 adult spleens were investigated. The expression of CD27 in combination with monoclonal antibodies against CD3, CD21, IgM, IgD and ASM-1 was analyzed by immunohistochemistry. The marginal zone was already present at 4 months after birth but CD21 expression was observed first after 2 years. CD27-positive marginal zone B cells were observed firstly 2 years after birth and increased in number to adult levels at the age of 5 years. We demonstrated that the MZ of infants and young children is populated by naive B cells, which are replaced by memory B cells in a time frame of 2 to 5 years. Before the age of 2 years, although present, memory B cells appear to be unable to colonize the marginal zone. Because of the absence of memory B cells in the marginal zone, the immune system of a child is not capable to initiate a rapid secondary humoral immune response comparable to the adult immune response.