Immunological Risk Factors in Recurrent Pregnancy Loss in Patients With Hereditary Thrombophilia.

BACKGROUND: Recurrent pregnancy loss (RPL) is a complicated reproductive disorder with underlying genetic and immunological causes. RPL may be influenced by hereditary thrombophilia, a class of blood clotting-related genetic abnormalities, via the vascular and immune systems. This study examines the immunological characteristics that hereditary thrombophilia patients have in common with RPL. METHODS: A prospective cohort study included 300 patients split into two groups: a control group without hereditary thrombophilia and a group with the condition. Interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and interferon-gamma (IFN-γ) levels were measured, along with demographic specifics, antiphospholipid antibodies, natural killer (NK) cell counts, and other cytokines. Group differences were found using statistical analysis. RESULTS: Antiphospholipid antibodies were significantly more common in the thrombophilia group (42% testing positive, p=0.001) compared to the control group (12% testing positive), despite demographic factors being similar between groups (p=0.372 and p=0.093). When body mass index (BMI) was taken into account, the study found a statistically significant difference (p=0.046), with the thrombophilia group having a higher mean BMI (26.3 kg/m2, standard deviation (SD): 2.8) than the control group (24.7 kg/m2, SD: 3.1). IL-6 (14.8 pg/mL, SD: 3.2, p=0.029) were higher than the control group (12.4 pg/mL, SD: 2.1), and TNF-α levels were higher in the thrombophilia group (10.5 pg/mL, SD: 2.0, p=0.012) compared to the control group (8.9 pg/mL, SD: 1.5), but NK cell counts did not differ significantly (p=0.213). CONCLUSION: This study emphasizes the role of elevated pro-inflammatory cytokines (IL-6 and TNF-α) and antiphospholipid antibodies in RPL among people with hereditary thrombophilia. In this population, early detection and immunomodulatory interventions may improve pregnancy outcomes. To fully comprehend these mechanisms and create customized treatments, collaborative research is required.

Unlocking the Uterine Code: Microbiota, Immune Cells, and Therapy for Recurrent Reproductive Failure.

The uterine microbiota has been the subject of increasing study, but its interaction with the local immune system remains unclear. Successful embryo implantation relies on endometrial receptivity, which is pivotal for immunological tolerance to fetal antigens and precise regulation of inflammatory mediators. Emerging data suggest a dynamic interplay between endometrial microflora and the immune system, making dysbiosis a potential determinant of pregnancy outcomes. Imbalances in the regulation of immune cells in the endometrium and decidua have been associated with infertility, miscarriage, and obstetric complications. A thorough comprehension of the immune system in the female reproductive tract shows potential for improving women's health and pregnancy outcomes. The objective of this study was to evaluate the patterns of endometrial microbiota in patients with recurrent implantation failure (RIF) and recurrent pregnancy loss (RPL) and to explore their implications for endometrial immune cells and chronic endometritis (CE). Immune cells in biopsies from 107 RIF and 93 RPL patients were examined using flow cytometry. The endometrial microbial composition was analyzed using real-time polymerase chain reaction (RT-PCR). The research uncovered disrupted endometrial microbiota in most women with RIF and RPL, which was often associated with significant effects on lymphocytes, T cells, and uNK cells.

Decreased ratio of FOXP3+/FOXP3-CD45RA+CD4+ T cells in peripheral blood is associated with unexplained infertility and ART failure.

Unexplained infertility has a huge social impact and is a significant challenge for both clinicians and researchers. Previous studies have shown the involvement of multiple factors in infertility. Among these, the subset of regulatory T cells is of particular interest for the maternal tolerance towards the semi-allogenic fetus. We investigated circulating CD45RA+ regulatory and non-regulatory CD4+ T cells in healthy women and patients with unexplained infertility in the context of thymic output and peripheral proliferation. The proportion of FOXP3+ and FOXP3-CD45RA+CD4+ T cells in peripheral blood was studied in control groups of healthy parous and nulliparous (never-pregnant) women and in patients with unexplained infertility. In the same groups thymic output and peripheral proliferation were defined by the sj/ßTREC ratio, and signal joint T-cell receptor excision circles (sjTREC) and Ki67 expression, respectively. In parous women a decrease in sjTREC/105 cells and CD45RA+ T lymphocytes, compared to nulliparous group was found. At the same time, the proportion of FOXP3-CD45RA+CD4+ cells, but not FOXP3+CD45RA+ Tregs was reduced. In contrast, in patients with unsuccessful pregnancy, proportions of both regulatory and non-regulatory T cell counterparts were lower. Taken together, our results provide evidence for group-specific properties in the CD45RA+ T cell compartment between healthy parous, nulliparous and women with unexplained infertility.

Interleukin-17 producing T cells could be a marker for patients with allergic rhinitis.

BACKGROUND: Interleukin-17A (I-17A)-producing CD4+T helper cells have been implicated in allergic inflammation; however, the role of IL-17A in allergic rhinitis (AR) patients with different degrees of atopy and airway reactivity to methacholine (Mch) has not been examined. OBJECTIVES: To explore IL-17A-producing CD3+CD4+T cells in peripheral blood of patients with persistent AR and assess the degree of atopy, eosinophil count (Eo count), and bronchial hyper-responsiveness (BHR) to methacholine. METHODS: The study involved 61 patients and 30 controls. The percentage of CD3+CD4+IL-17A+T cells in peripheral blood was measured by flow cytometry, bronchial challenges with Mch were performed, as were skin prick tests with standard inhalant allergens, and Eo count was measured. Atopic status was determined by the number of positive SPT results and wheal mean diameter. RESULTS: A statistically significant difference in Th17 cell percentage was found in the AR and control groups (2.59 +/- 1.32% and 1.24 +/- 0.22% respectively, P = 0.001). Forty-one patients (67.2%) were polysensitized to indoor and outdoor allergens, while 20 (32.8%) had positive skin prick tests to indoor allergens. CD4+T cells were significantly higher in the patient group compared to the control group (2.91 +/- 1.5% versus 1.91 +/- 0.62%, P = 0.005), as was Eo count (4.48 +/- 2.13 vs. 2.32 +/- 1.83) (P = 0.0001). Forty-one in the AR group (67%) and 7 (23%) in the control group were Mch-positive (P = 0.001). The percentage of IL-17A-producing CD4+T cells was significantly higher in males compared to females (3.15 +/- 1.8% versus 2.31 +/- 0.9%, P = 0.02) CONCLUSIONS: Polysensitized AR patients exhibited higher IL-17A-producing CD4+T cell levels and eosinophil counts. Male patients displayed a higher frequency of IL-17A-producing T cells.

Inherited thrombophilia and IVF failure: the impact of coagulation disorders on implantation process.

In connection with the embryo acceptance process after IVF procedure, endometrial cells surface receptors, extracellular matrix (ECM) molecules, endothelium and blood circulation factors were involved in remodelling of endometrium. Plasminogen activator inhibitor type 1 plays a significant role during the early phases of placental vascular remodelling and regulates the trophoblast invasion through controlling plasmin activity. Endometrial cell surface protein integrin alphaV/beta3, responsible for the adhesion of the embryo, has had also the same subunit beta3, which is component of integrin alphaIIb/beta3 connected with platelet aggregability. Prothrombin, furthermore, has had a debatable effect upon endothelial and mesenchymal cells and possible contribution on embryo vascular development. Confoundable data have been present about the role of coagulation factor V and its role for implantation. These and other coagulation factors have relatively common gene polymorphisms that enhanced their activity. This review discusses the effect of increased coagulation activity on implantation process, which is not yet fully determined. The establishment of the positive or negative impact of mother hypercoagulability on the success of embryo implantation after assisted reproduction technology could determine the timing of preventing anticoagulant therapy in women with history of early embryo loss.

Anti-fibrillin-1 autoantibodies in normal pregnancy and recurrent pregnancy loss.

PROBLEM: The aim of this study was to investigate anti-fibrillin-1 autoantibody in patients with a history of recurrent pregnancy loss (RPL) and during normal pregnancy. METHOD OF STUDY: Anti-fibrillin-1 IgG and IgM antibodies were measured by a home made ELISA in serum samples of 48 medically and obstetrically normal pregnant women, classified to three trimester groups, 15 female patients with RPL and 26 healthy non-pregnant women classified to two control subgroups: (a) women who had already had at least one previous successful pregnancy and (b) women who had never been pregnant. Differences in anti-fibrillin-1 autoantibodies between the groups were analyzed for statistical significance (P<0.05) with one-way analysis of variance (ANOVA) and multiple comparison test - Post Hoc test, Least Significant Difference method. RESULTS: Anti-fibrillin-1 IgM autoantibodies were significantly decreased in the second and third trimester pregnant women compared to the nulligravida controls. RPL patients had significantly increased anti-fibrillin-1 IgM antibody compared to control group (a). CONCLUSION: Fibrillin-1 degradation seems to be decreased during the second and third trimester of normal pregnancy. Increased anti-fibrillin-1 IgM antibodies in RPL patients may be a secondary phenomenon of increased fibrillin-1 degradation and contribute to the pathogenesis of pregnancy losses.

Levels of platelet-leukocyte aggregates in women with both thrombophilia and recurrent pregnancy loss.

The aim of our study was to investigate the significance of platelet-leukocyte aggregates (PLA) in women with recurrent pregnancy loss (RPL) as well as to identify association between common thrombophilic factors and whole blood levels of PLA in these patients. We measured PLA by whole blood flow cytometry in 66 nonpregnant women with hereditary and/or acquired thrombophilia and RPL, classified to 3 study groups, according to the type of losses (first, second, and third trimester) and 35 age-matched healthy controls. Platelet-leukocyte aggregates levels in all study groups were significantly increased compared to the control group (median values 2.13%, 2.32%, and 2.41%, vs median value in the control group 1.39%, P < .05 for all comparisons). Women with a single thrombophilic factor and women with combination of thrombophilic factors did not differ significantly as regards the PLA levels (2.13% vs 2.27%, P = .4). This study suggests that PLA may have a role in the pathogenesis of RPL in women affected by hereditary or acquired thrombophilia.

Polymorphism A1/A2 in the cell surface integrin subunit ß3 and disturbance of implantation and placentation in women with recurrent pregnancy loss.

Polymorphism A1/A2 in the ß3 subunit of integrins αIIb/ß3 and αV/ß3 is implicated in the risk of development of embryonic and fetal recurrent pregnancy loss (RPL). In 191 women with RPL, polymorphism A1/A2 was statistically significantly associated with RPL at <10 weeks of gestation (29.3% versus 16.4% in controls), but it was much more pronounced in 67 women with RPL between 10 and 20 weeks of gestation (41.8%), illustrating its role in recurrent fetal loss.

The role of NK cells in the autoimmune thyroid disease-associated pregnancy loss.

Pregnancy loss is a frequent event. Autoimmune thyroid disorders and altered natural killer (NK) cell functions are two distinct risk factors, which independently could induce adverse pregnancy outcome. Thyroid autoimmunity has been an object of increased attention by investigators in the context of pregnancy loss. Peripheral NK cells and uNK cells comprise distinct cell populations in terms of phenotype and function but they play an important role in the course of a normal human pregnancy via several potential functions. In autoimmune thyroid diseases, several abnormalities of killer cell activity have been described. The functional defects involving NK maturation and/or functional activation observed in Graves' disease patients could independently influence the reproductive outcome. This suggestion needs extensive investigation and could be important for the therapeutical approach in preventing pregnancy loss in patients with thyroid autoimmunity.

Age-related changes of anti-elastin antibodies in senescence-accelerated mice.

BACKGROUND: Antibodies recognizing the elastin precursor tropoelastin (ATEAb) or degradation products alpha-elastin (AEAb) are found in the serum of healthy human subjects, as a part of a homeostatic mechanism which assembles new or clears altered elastin structures. Serum ATEAb (reflecting elastin synthesis) and AEAb (reflecting elastin destruction) appear to correlate with the production and breakdown of the elastic tissue, respectively. OBJECTIVE: The aim of this study was to investigate plasma levels of AEAb and ATEAb in senescence-accelerated prone (SAMP8) and senescence-accelerated resistant (SAMR1) mice, compared with imprinting control region (ICR) mice in order to evaluate their age-related changes. METHODS: The levels of AEAb and ATEAb were measured by home-made ELISA in plasma of SAMP8, SAMR1, and ICR mice, grouped according to their age (3 and 9 months) and sex. The specificity of AEAb and ATEAb activity in mouse plasma, and elastin-derived peptides (EDP) in sera of ICR mice at 3 and 9 months of age were tested by competitive ELISA. RESULTS: The specificity of AEAb and ATEAb in mouse plasma was confirmed by the competitive investigations. The levels of AEAb in the plasma of SAMR1 and SAMP8 were increased compared to the levels measured in ICR on the matched ages (p < 0.001). Age-related increase of the levels of AEAb and ATEAb was established in the 3 strains (p < 0.001). Significantly higher levels of AEAb were established in female 9-month-old mice compared to males in all strains. The ATEAb:AEAb ratio was significantly lower in the SAM compared to the ICR strain. Positive correlation was established between the levels of serum AEAb and EDP in mouse sera of ICR mice. CONCLUSION: Variations with age in the plasma levels of AEAb and ATEAb were established in SAM compared with ICR, and in SAMP8 compared with SAMR1. Our findings suggest that increased anti-elastin IgG autoantibodies could be used as a marker of aging in SAM and possibly contribute to the processes of aging. The absence of a difference between SAMP8 and SAMR1 regarding the ATEAb:AEAb ratio raises the question if SAMR1 are an appropriate control of SAMP8 in terms of the senescence of the elastic tissues.

Flow cytometric investigation of CD40-CD40 ligand system in preeclampsia and normal pregnancy.

Our aim was to investigate the CD40-CD40 ligand system in preeclamptic women. We also studied CD62P and platelet-monocyte aggregates, which have been closely linked to the CD40-CD40L system. Platelet expression of CD40L and CD62P and expression of CD40 on monocytes and platelet-monocyte aggregates were determined by flow cytometry in whole blood from 23 preeclamptic women, 23 normotensive pregnant women, and 23 nonpregnant women. The preeclamptic women showed a significant increase in CD40L and CD62P on platelets and in CD40 on monocytes when compared with normotensive pregnant women and nonpregnant women (all P < .001). There was a significant increase in platelet-monocyte aggregates in preeclamptic women (P < .001) and normotensive pregnant women (P = .003) compared with nonpregnant women. Preeclampsia is associated with activation of the CD40-CD40L system. The activation of this system may contribute to the development or maintenance of the proinflammatory and prothrombotic milieu found in preeclampsia.

Association of inherited thrombophilia with embryonic and postembryonic recurrent pregnancy loss.

To investigate the impact of maternal-inherited thrombophilia: effects of factor V Leiden (FVL) and prothrombin gene mutation (FII 20210G>A) on the development of recurrent pregnancy loss in embryonic and postembryonic periods. A total of 153 patients were analysed for FVL and FII 20210G>A according to placenta gestation: 94 women with embryonic loss prior 10 weeks of gestation and 59 women with postembryonic (early fetal) loss occurring between 10 and 14 weeks of gestation. The control group consisted of 100 healthy women, with at least one uncomplicated full-term pregnancy. FVL prevalence was not significantly associated with pregnancy loss prior to 10 weeks of gestation (9.6%) compared with controls (7%) [odds ratio (OR) 1.41; 95% confidence interval (CI) 0.454-4.416, P > 0.05], but it was much more pronounced in women with postembryonic loss (10-14 weeks of gestation) - 18.6% (OR 3.05; 95% CI 1.010-9.387, P = 0.047). FII 20210G>A was significantly higher in both groups with embryonic (17%) and early fetal losses (16.9%) as compared to controls (3%) (OR 6.63; 95% CI 1.731-29.752, P = 0.003; OR 6.60; 95% CI 1.572-31.856, P = 0.006). FII 20210G>A is significantly associated with an increased risk of early recurrent pregnancy loss throughout the entire first trimester. FVL was significantly higher only in early fetal period after starting of the placentation process, but not associated with embryonic recurrent pregnancy loss. These results suggested that the first trimester should be viewed rather as a heterogeneous interval, with different relation to FVL in the embryonic and postembryonic fetal period. Genetic testing should be applied according to the diverse contribution of thrombophilic markers to embryonic and postembryonic period.

Upregulation of the CD40-CD40 ligand system in pre-eclampsia.

OBJECTIVE: To investigate the CD40-CD40 ligand (CD40L) system in women with pre-eclampsia. METHODS: Expression of CD40 on monocytes and expression of CD40 and CD40L on platelets were determined by whole blood flow cytometry in 23 women with pre-eclampsia and in 23 normotensive pregnant women. Serum levels of soluble CD40L in both groups of women were measured by enzyme-linked immunosorbent assay. RESULTS: There was a significantly higher expression of CD40 and CD40L on platelets and CD40 on monocytes in the women with pre-eclampsia compared with normotensive pregnant women (P<0.001 for all comparisons). The serum concentration of soluble CD40L was significantly higher in women with pre-eclampsia compared with normotensive pregnant women (P=0.012). CONCLUSION: Pre-eclampsia is associated with activation of the CD40-CD40L system. The activation of this system may contribute to the development or maintenance of the proinflammatory and prothrombotic responses, increased cytokine production, and endothelial cell dysfunction found in pre-eclampsia.

Anti-elastin antibodies and elastin turnover in normal pregnancy and recurrent pregnancy loss.

PROBLEM: The aim of this study was to investigate elastin turnover and autoimmunity in patients with a history of recurrent pregnancy loss (RPL) and during normal pregnancy. METHOD OF STUDY: Anti-alpha-elastin and anti-tropoelastin IgG and IgM antibodies were measured by a home-made ELISA in serum samples of 60 medically and obstetrically normal pregnant women, classified to three trimester groups, 18 female patients with RPL and 18 healthy non-pregnant women with a history of successful pregnancies. One way analyses of variance and Least Significant Difference method were used for a statistical analysis. RESULTS: Anti-alpha-elastin IgG autoantibodies were significantly decreased in the third trimester pregnant women. IgM anti-alpha-elastin autoantibodies were significantly decreased in all pregnancy groups compared with the controls. Synthesis/degradation ratio of elastin was significantly increased in the third trimester pregnancy group, suggesting decreased elastin degradation during this period of pregnancy. Comparing the RPL patients with the healthy non-pregnant controls showed a significantly increased anti-alpha-elastin IgG antibody and significantly decreased synthesis/degradation ratio in the patient's group, suggesting increased elastin degradation in RPL. CONCLUSION: Elastin degradation is decreased during normal pregnancy. Increased anti-elastin IgG antibodies may contribute to the pathogenesis of pregnancy losses.

Non-enzymatic glycation of human fibrillin-1.

Non-enzymatic glycation of proteins is one of the key mechanisms in the pathogenesis of diabetic complications and may be significant in the age-related changes of tissues. We isolated and investigated the in vitro glycation of human aortic fibrillin-1. Fibrillin-1 was prepared from thoracic aortas of 9 accident victims distributed in three age groups. The purity of isolated fibrillin-1 was proved. It was glycated by incubating with different glucose concentrations in 0.2 M phosphate buffer, pH 7.4, for 30 days, at 37 degrees C. The degree of early products of glycation was measured by two colorimetric methods, i.e. nitroblue tetrazolium and 2-thiobarbituric acid. Advanced glycation end products (AGEs) were determined by fluorescence measurement. The highest level of early products of glycation was found on day 2 after the beginning of incubation for the fibrillin-1 isolated from the youngest group. Fluorescence in the age groups, as an index of advanced glycation, consistently increased between days 6 and 24. The fibrillin-1 isolated from the youngest group had the highest capacity to form fructosamine and AGEs under glycation in vitro. The capacity of glycation of the 'oldest' fibrillin did not increase significantly during the incubation. Investigation of the properties of glycated fibrillin-1 will help to understand the importance of this long-lived protein to age-related changes in tissues and for diabetic complications.

Idiotypic and anti-idiotypic elastin autoantibodies: Implications for IVIg and pregnancy loss.

PROBLEM: The aim of this study was to investigate anti-elastin and anti-anti-elastin autoantibodies in intravenous immunoglobulin (IVIg) lots as an attempt to further explain the effect of IVIg in recurrent pregnancy loss (RPL). METHOD OF STUDY: Serum samples of 10 female patients with RPL and 10 healthy subjects were tested for anti-elastin autoantibodies and used in competitive inhibition studies. A total of 44 IVIg lots (ZLB Behring, Switzerland) were tested for anti-elastin and anti-anti-elastin idiotypes. One way analysis of variance (ANOVA) and Least Significant Difference (LSD method) were used for statistical analysis of differences between the lots. RESULTS: Serum anti-elastin IgG autoantibodies were significantly higher in the study group, compared to the controls. In all lots anti-elastin IgG antibodies were identified. All lots (except two of them) showed similar dose-dependent inhibition of serum anti-elastin activity by anti-elastin anti-idiotypes in IVIg. CONCLUSIONS: Anti-elastin IgG autoantibodies were increased in patients with RPL - a finding which needs further explanation. Anti-elastin and anti-anti-elastin idiotypes were identified in different IVIg lots. The presence in IVIg of anti-idiotypes against anti-elastin autoantibodies from patients' sera could be an additional mechanism of the beneficial effect of IVIg in reproductive failure.

Autoantibodies and prediction of reproductive failure.

PROBLEM: To determine which autoantibodies are associated with reproductive failure. METHOD OF STUDY: Sera from 269 patients with autoimmune disease and/or reproductive failure were analyzed for anti-phospholipid (aPL), anti-annexin-V, anti-lactoferrin, anti-thyroglobulin, anti-thyroid peroxidase, anti-prothrombin, anti-nuclear, and anti-saccharomycetes cerevisiae antibodies (ASCA), by enzyme-linked immunosorbent assay. Patients were classified as: recurrent pregnancy loss (RPL), infertility, and autoimmune diseases. The results were compared with those of 120 healthy volunteers. RESULTS: In autoimmune diseases, the prevalence of anti-prothrombin, anti-annexin, anti-phospholipid and anti-nuclear antibodies was significantly higher than in the control group, OR 11.0 [CI, 3.5-35.2], 33 [CI, 7.2-174.2], 13 [CI, 1.4-309.7], and 16.1 [CI 2.4-122], respectively. In infertility, the antibodies with significantly higher levels than controls were: aPL OR, 5.11 [CI 1.2-25.4], and anti-prothrombin antibodies, OR, 5.15 [CI, 2.1-12.7]. In RPL, ASCA, anti-prothrombin and aPL were more prevalent than in controls, OR 3.9 [CI, 1.5-10.6], 5.4 [CI, 2.4-12.5] and 4.8[CI, 1.2-22.2] for each antibody, respectively. Anti-prothrombin antibodies and aPL were more significantly associated with late pregnancy losses than early losses. CONCLUSION: ASCA antibodies have not previously been described in RPL. Nor are anti-prothrombin antibodies usually assessed in infertility or RPL. If these results are confirmed in further studies, these antibodies might be assessed routinely in reproductive failure.

Intravenous immunoglobulin therapy in antiphospholipid syndrome.

Antiphospholipid syndrome (APS) is an autoimmune disorder defined by the occurrence of venous and arterial thromboses and pregnancy morbidity, frequently accompanied by a moderate thrombocytopenia, in the presence of antiphospholipid antibodies. There is both laboratory and clinical evidence for the beneficial role of intravenous immunoglobulin (IVIg) in APS. Data on the use of IVIg in patients with APS have focused on its obstetric complications and antiphospholipid antibodies-positive patients undergoing in vitro fertilization, but there are also case reports about treatments of other clinical manifestations (mainly hematological) of the syndrome. Future research should determine when to use anticoagulation, IVIg, or both in the treatment of APS.

Age-related changes in the glycation of human aortic elastin.

Non-enzymatic glycation of proteins is a consequence of hyperglycemia in diabetes and correlates with aging. The aim of the study was to investigate age-related changes in the glycation of human aortic elastin in healthy subjects by two approaches: (1) assessment by fluorescence method of formed in vivo advanced glycation end products (AGEs) of elastins, purified from human aortas, obtained from different age groups; (2) in vitro glycation of elastins from different age groups and investigation of their capacity to form early (by colorimetric nitroblue tetrazolium method) and AGEs (fluorescence method). Human insoluble elastins were prepared from macro- and microscopic unaltered regions of thoracic aortas, obtained from 68 accident victims, distributed in 15 age-groups, using the method of Starcher and Galione. Soluble alpha-elastins were obtained by the method of Partridge et al. The direct assessment of Maillard reaction related fluorescence in the age groups showed increase of the fluorescence with age. The 'young' elastin had the highest capacity to form both fructosamine and AGEs under glycation in vitro. The glycation of 'old' elastin did not increase markedly during the incubation. These results are consistent with the interpretation that because of its long biological half-life, elastin is susceptible to the slow process of glycation and the following modifications would contribute to the age-related changes of connective tissue.