Ileana Malan Borel

Paradoxical behavior of asymmetric IgG antibodies

Summary: Changes in the quantity and quality of antibodies occur in the course of an immune response. This review describes the physicochemical and biological properties of asymmetric antibodies as well as their functions, beneficial or harmful to the host, according to the nature of the antigen and the particular situation in which they act. Asymmetric antibodies have two paratopes, one of high affinity, with K0 similar to that of symmetric antibodies, and the other one with an affinity for the antigen 100 times lower. Functional univalence is due to steric hindrance present in one of the paratopes by the carbohydrate moiety attached to the Fd fragment of the Fab region, so these antibodies are unable to form large antibody‐antigen complexes and cannot trigger reactions, such as complement fixation, phagocytic activity and antigen clearance. When asymmetric IgG antibodies are specific for self‐antigens, they prove beneficial for the host by exerting regulatory functions. In allergic manifestations, in autoimmune diseases and especially during pregnancy, despite the fact that the antigens responsible for the process are foreign to the host, they also perform beneficial activity During pregnancy, the placenta secretes molecules or factors that regulate the synthesis of these antibodies, thus favoring fetal protection.

Preferential synthesis of asymmetric antibodies in rats immunized with paternal particulate antigens. Effect on pregnancy.

The effect of immunization of female Fischer rats with particulate (spleen cells) (group I) or soluble (supernatant of disintegrated spleen cells) (group II) paternal antigens previous to mating with Buffalo rats was investigated. The percentage of asymmetric IgG molecules in the serum of rats inoculated with particulate antigens was 38% while in those injected with soluble antigens it was 29% and 28% in non-immunized animals. These percentages further increased during pregnancy to 45%, 38% and 37%, respectively. The antipaternal antibody titres, as determined by indirect immunofluorescence (IIF), was much higher in the animals immunized with particulate antigens but the effector activity, judged by complement fixation, was similar in both groups. The same values were observed at the time of mating (after 3 months of immunization) and at day 17 of pregnancy. Fetus and placenta weights and offspring survival were equally greater in group I than in group II or non-immunized rats (group III). The results obtained indicate the preferential synthesis of antipaternal IgG asymmetric antibodies in rats injected with particulate antigens previous to mating and suggests a beneficial effect of these antibodies in pregnancy.

Modulation of the Immune Response by Progesterone-Induced Lymphocyte Factors

Rat spleen and peripheral blood lymphocytes express progesterone receptors whose concentration is increased greatly during the early phase of pregnancy. After stimulation of progesterone the expression of receptors was augmented 2–3 times. When cells were cultured in the presence of progesterone they released a soluble factor that inhibited cellular immunoreactions (MLR, CRC) and cellular proliferation as measured by thymidine incorporation by spleen‐cell culture. This factor also inhibited the synthesis of anti‐DNP antibodies by a mouse hybridoma and diminished the proportion of cells in phase S. However, the percentage of asymmetric molecules produced by the hybridoma remained unaltered. These results support the hypothesis that soluble factors released by rat lymphocytes modulate the immune response of the mother and participate in the mechanism that protects the fetus against antipaternal antibodies.

The proportion of symmetric and asymmetric IgG antibody molecules synthesized by a cellular clone (Hybridoma) can be regulated by placental culture supernatants

The purpose of the present work was to establish whether the placenta is producing factors favoring an increased synthesis of asymmetric IgG antibodies which are known to assume a protective effect upon paternal antigens to which they largely are specific. In this way they can contribute to fetal survival in the maternal uterine environment. The hybridoma cell lines OKT8 (anti-CD8) and 112B4 (anti-DNP) were used in this respect since they synthesized both symmetric and asymmetric molecules of the IgG2a and IgG1 subclasses, respectively, murine isotypes in which anti-paternal antibodies have been detected. The cells were cultured in RPMI 1640 medium supplemented with 10% BCS and different amounts (5, 10, and 20%) of human placental supernatant. After incubation for 3 days at 37 degrees C in a humid chamber containing 5% CO2 the cells were centrifuged and the antibodies were obtained from the culture medium by a purification procedure involving precipitation at 50% ammonium sulfate saturation followed by DEAE-cellulose chromatography. Symmetric and asymmetric antibodies were separated by Con A-Sepharose affinity chromatography, the latter lectin retaining selectively only asymmetric IgG molecules. Both OKT8 and 112B4 hybridomas presenting a stable background synthesis of 15-17% of asymmetric antibodies have shown an increased level reaching 27-28% of these molecules in the presence of 5-10% placental supernatant added to the RPMI 1640 culture medium. These results clearly show that placental factors can up-regulate efficiently the synthesis of asymmetric IgG molecules of different isotypes secreted by plasma cells.

Expression of HLA-G and MICA mRNA in renal allograft.

HLA-G is a nonclassical MHC class I antigen that displays tolerogenic functions; MICA is a stress-regulated molecule recognized by NKG2D cytotoxicity-activating receptor expressed by NK and T cells subsets. We evaluated HLA-G isoforms and MICA mRNA levels in peripheral blood mononuclear cells (PBMCs) and in biopsies from kidney allograft recipients with acute rejection (AR), chronic rejection (CR), and stable graft evolution (SE). HLA-G1 was the only transcript resulted from amplification, both in PBMCs as in biopsy samples. HLA-G1 mRNA levels in PBMCs from 9/10 patients with CR, 7/9 with AR and 8/10 healthy volunteers were below the median value of SE patients. The analysis of biopsies revealed that patients with AR (n=6), who overcame rejection had a tendency towards higher HLA-G1 levels than those with nephrotoxic acute tubular necrosis (ATN) (n=3). Similar levels of MICA expression were observed in PBMCs from AR, CR, SE and C groups; MICA expression levels were similar also in biopsy specimens from AR and nephrotoxic ATN patients. No correlation was found between MICA expression and the graft state. These preliminary results suggest that HLA-G1 isoforms, but not MICA mRNA levels, may provide a marker for measuring the state of kidney allograft, and be the basis for further studies that may establish the influence of these molecules in renal allograft rejection or acceptance.

Modulation of the humoral immune response by placental secretory factors.

PROBLEM: To investigate how the factors secreted by human placenta modify the quality and the quantity of the antibody produced by the hybridoma as well as its cellular proliferation.

Effect of Rat Placental Culture Supernatants on Cellular and Humoral Immune Responses

PROBLEM: To evaluate the effect of rat placental culture supernatants (PS) on spontaneous, mitogen‐ and alloantigen‐induced lymphoproliferation, antibody synthesis regulation, and symmetric/asymmetric antibody ratio.

Effects of isomeric fatty acids on reproductive parameters in mice.

Problem  The aim of this study was to determine if dietary fatty acids (FA) level or isomeric FA type may affect reproductive parameters in mice.

Ontogenic evolution of chicken red cell Fc receptor.

Abstract The ontogenic evolution of chicken red cell Fc receptor was studied in red cells from different age chicken embryos, baby chicken, and adult chicken. The Fc receptor binding capacity for ligands, the number of Fc receptors by red cell, and the association constant between receptor and ligand were analyzed. The Fc receptor is expressed in the red cell surface of 6-day chicken embryo and its binding capacity for ligand—minimal at this moment—is increased in the 8-day chicken embryo red cells. The 12-day chicken embryo erythrocytes binding capacity is similar to the adult chicken red cells. The number of Fc receptors by red cell increase with the age of chicken embryo. After 9 days this number is not modified and it is the same as in adult chicken. Variations of Ko and binding capacity for ligands show a similar evolution in embryogenic development. From these data we suggest that although on Day 9 the number of receptors per cell is the same as in adult chicken, the receptors are not completely exposed at this time and as a consequence, their binding capacity for ligands is lower than in adult chicken erythrocytes.