Suppression of the formation of cells secreting antibodies and antigen-dependent nonspecific immunoglobulins in mice receiving isologous antierythrocyte immunoglobulins

Mice injected with syngeneic cellulose-conjugated immunoglobulins (Ig) containing antibodies to sheep red blood cells (SRBC) develop a specific non-responsiveness to SRBC. Such animals demonstrate a sharp decrease not only in the formation of anti-SRBC antibody producers but also of the cells secreting antigen-dependent nonspecific Ig. The inhibition of both these processes is antigen-specific. It is suggested that inhibition of the cells forming antigen-dependent nonspecific Ig is due to suppression of either hypothetic inductors or precursors of these cells expressing an idiotype spectrum similar to that of anti-SRBC antibody producers.     

Relation of the formation of producers of antigen-dependent nonspecific immunoglobulins to the dose of T-dependent and T-independent antigens

The dependence of the production of antibody-forming cells (AFC) and non-specific immunoglobulin-forming cells (nIFC) on the doses of T-dependent (sheep red blood cells, SRBC) and T-independent (polyvinylpyrrolidone, PVP and pneumococcal polysaccharide SSS III) antigens was investigated. The immunization of BALB/c mice with immunogenic or subimmunogenic doses of SRBC and PVP induced a marked increase in the number of antigen-dependent nIFC. In contrast, the injection of any SSS III doses did not influence the amount of nIFC, although a specific immune response to SSS III was quite obvious. Thus, two T-independent antigens, type II, differ in their ability to induce non-specific immune reactions. The experiments on simultaneous administration of monoclonal anti-Thy-1.2 antibodies and PVP or SSS III to mice have demonstrated that these differences were not related to T-suppressor activity. The possible role of T helpers in the immune response to T-independent antigens is discussed.     

Suppressor cells in tumor-bearing mice capable of nonspecific blocking of in vitro immunization against transplant antigens.

Spleen cells from mice with progressively-growing methyl-cholanthrene-induced tumors, when immunized in vitro against transplant alloantigens, developed less cytotoxic activity against these antigens as measured by a short-term chromium-release assay than did spleen cells from normal mice. The hyporesponsiveness of spleen cells from the tumor-bearing mice seemed to be due to the presence of suppressor cells which could be removed by nylon-column passage but not by anti-theta treatment and which, in mixture experiments, could inhibit the response of normal spleen cells. The suppression appeared to occur at the sensitization stage and not at the effector stage of the in vitro tests. No evidence was found for mediation of the suppression by soluble factors. These observations emphasize the growing importance of suppressive mechanisms in tumor immune systems.     

Plasmid vector-linked maturation of natural killer (NK) cells is coupled to antigen-dependent NK cell activation during DNA-based immunization in mice

Plasmid DNA vaccines serve in a wide array of applications ranging from prophylactic vaccines to potential therapeutic tools against infectious diseases and cancer. In this study, we analyzed the mechanisms underlying the activation of natural killer (NK) cells and their potential role in adaptive immunity during DNA-based immunization against hepatitis B virus surface antigen in mice. We observed that the mature Mac-1(+) CD27(-) NK cell subset increased in the liver of mice early after DNA injection, whereas the number of the less mature Mac-1(+) CD27(+) NK cells in the liver and spleen was significantly reduced. This effect was attributed to bacterial sequences present in the plasmid backbone rather than to the encoded antigen and was not observed in immunized MyD88-deficient mice. The activation of NK cells by plasmid-DNA injection was associated with an increase in their effector functions that depended on the expressed antigen. Maturation of NK cells was abrogated in the absence of T cells, suggesting that cross talk exists between NK cells and antigen-specific T cells. Taken together, our data unravel the mechanics of plasmid vector-induced maturation of NK cells and plasmid-encoded antigen-dependent activation of NK cells required for a crucial role of NK cells in DNA vaccine-induced immunogenicity.     

Role of dendritic cells in the immune response to T-independent antigens of type 2

Dendritic cells (DC) belong to the most effective antigen-presenting cells. Their role in the presentation of thymus-dependent antigens and initiation of primary immune response is well known. At the same time, participation of DC in the immune response to T-independent antigens of type 2 (TI-2 antigens) is poorly explored. In this work, the ability of DC to initiate the immune response to a TI-2 antigen α(1→3) dextran (Dex) is investigated. Mouse bone-marrow-derived DC were generated by culturing the precursors with GM-CSF and then DC were pulsed by TI-2 antigens. The pulse induced DC activation, as was verified by an increase in the number of CD80 and CD86 positive cells. Uptake of FITC-labeled Dex was examined by flow cytometry. At a concentration of FITC-Dex of 100 μg/10⁶ cells, the number of DC binding the antigen (Ag) reached “plateau”. DC charged by TI-2 antigens were mixed with normal mouse splenocytes and cultivated in RPMI-1640 medium for 4 days. The numbers of antibody- and immunoglobulin-forming cells were determined by ELISPOT method. The mixtures of splenocytes and naïve DC not charged by the Ag were used as control. It was shown that the increase in the numbers of AFC and IFC under the influence of naïve DC did not exceed 20%. On the contrary, the addition of DC pulsed by the Ag increased specific immune response more than twofold. The data obtained point to the direct interactions of DC with TI-2 antigens. Pulsed DC present TI-2 antigens to mouse splenocytes and induce specific and polyclonal B-cell activation, i.e., possess immunostimulating activity.     

Production of monoclonal antibodies to T-independent type 2 antigens with OptiMem-Iscove medium

To obtain monoclonal antibodies to T-independent antigens of type 2, having low immunogenicity and incapable of inducing the appearance of memory cells, the use of the medium OptiMem-Iscove (1:1) with 10% of fetal serum, glutamine (50 mM) and antibiotics (100 units/ml) is proposed. The main advantage of this medium is the possibility of cloning cells without the use of feeders. The method has been approved in the process of obtaining monoclonal antibodies (McAb) to TI-2 antigens, both bacterial (S3) and synthetic (PVP), as well as to McAb to T-dependent antigen (alpha-chains of human IgA).     

Role of G0- and G1-splenocytes and antigen-binding lymphocytes in the production of antigen-dependent nonspecific immunoglobulins

Immunization of irradiated and syngeneic splenocyte-treated CBA mice with bovine red blood cells stimulated the formation of both antigen-producing cells (APC) and antigen-dependent nonspecific immunoglobulin-producing cells (NIGPC). The injection of G0-cell-enriched, instead of normal, splenocytes (together with bovine RBC) to irradiated mice reduced by half the production of antigen-dependent NIGPC. Thus, it is evident, that some of them are formed from preexisting blast cells (G1). An additional removal of antigen-binding cells (ABC) from G0 lymphocyte population produced a still greater reduction in NIGPC formation (the increment was 92.3% lower than in the control). It is concluded that antigen-dependent NIGPC are formed both due to specific antigen-stimulation of G0 cells aid to nonspecific stimulation of blast cells with factors produced by antigen-stimulated T-cells.     

Effect of rubomycin and carminomycin on antibody formation during the immunization of mice with various antigens

The maximum immunodepressive effect of rubomycin and carminomycin was observed when the antibiotics were administered intravenously 24 hours after the immunization. The immune response induced by the sheep erythrocytes or the lipopolysaccharide was equally inhibited by rubomycin. Carminomycin in a dose of 0.5 mg/kg (0.1 of the LD50) to a larger extent inhibited the immune response stimulated by the lipopolysaccharide. Dependence of the immunodepressive effect of the antibiotics on their dose was found when the drugs were administered intravenously or orally.     

Immune responses to T-dependent and T-independent antigens during visceral leishmaniasis in mice: evidence for altered T-cell regulation of immune responses to non-parasite antigens

Antibody responses to T-dependent and T-"independent" antigens were studied in disease-susceptible (BALB/c and C57BL/10) and disease-resistant (A/J) mice infected with Leishmania donovani chagasi. Disease-susceptible mice but not disease-resistant mice showed a transient decrease in PFC responses to TNP on a T-dependent carrier (BGG) during the period of 4-8 weeks after infection. Infected disease-susceptible animals also showed increased responses to TNP on a type II T-independent carrier (Ficoll), which persisted until at least 14 weeks after infection. The increased responses were associated with a significant increase in anti-TNP antibody of the IgG2b subclass. When T-enriched spleen cells from infected mice and B-enriched spleen cells from uninfected mice were transferred to irradiated recipients immunized with TNP-Ficoll, increased anti-TNP PFC were observed over numbers seen in irradiated recipients which received both B and T cells from uninfected mice. Increased responses to TNP-Ficoll were also induced by prior administration of soluble leishmania extract in CFA. Infected mice immunized with TNP-LPS, a T-independent type I antigen, also had increased anti-TNP antibody responses, but had normal anti-LPS antibody responses. The elevated antibody production which occurred in response to the T-"independent" antigens could not be attributed to the relatively low polyclonal response which occurred in both disease-resistant and disease-susceptible mice infected with L. donovani chagasi. The observations are consistent with leishmania induced, transient alterations in some T-cell functions including response to haptens on T-dependent carriers, and a lack of down regulation of T-"independent" responses. Subtle lesions in immunoregulation may be important correlates of successful protozoal infection and may be responsible for some of the immunologic manifestations of the disease.     

Specific and nonspecific interactions of antibodies and immunoglobulins with antigens and the methods of analysis of these interactions

The problem of specific and nonspecific interaction of serum immunoglobulins and antigens was considered. It was shown that high-sensitive methods allow to reveal low-affinity non-specific interaction of immunoglobulins and antigens. If the concentration of the specific antibodies in a studied sample of serum is low, the non-specific interaction of serum immunoglobulins may exceed substantially the effect of specific reaction. In this case the obtained results could be misinterpreted. In this connection the conclusion has been done that in such a case it is necessary to take into account the capability of serum immunoglobulins to interact non-specifically with antigens and to discriminate between specific and non-specific interaction. The methods of the diminishing the non-specific interaction are suggested.