Role of activation in alveolar macrophage-mediated suppression of the plaque-forming cell response.

Alveolar macrophages (AM) are highly suppressive of the in vitro plaque-forming cell (PFC) response of spleen cells obtained from mice primed with sheep erythrocytes. Comparison of macrophage populations obtained from disparate anatomical sites revealed that although in both cases there was a cell-concentration-dependent suppression of the PFC response, resident AM or AM activated as a result of intravenous injection of Mycobacterium bovis BCG were equally suppressive at the doses examined. Although there was a similar dose-dependent suppression with peritoneal macrophages, BCG-activated cells were more suppressive of the PFC response than were resident cells. In contrast, splenic macrophages at comparable concentrations were not at all suppressive. Resident AM exhibited significantly lower levels of 5'-nucleotidase activity than did resident peritoneal macrophages. Macrophage-mediated suppression of the in vitro PFC response could not be attributed to the release of toxic oxygen metabolites (H2O2, O2- ,and .OH) or prostaglandins, since the addition of catalase, superoxide dismutase, 2-mercaptoethanol, or indomethacin did not completely reverse suppression. These results suggest that the lung microenvironment may maintain AM in an activated state which contributes to their potential immunoregulatory functions.     

Immune response mediated by liposome-associated protein antigens. I. Potentiation of the plaque-forming cell response.

Mice, immunized with liposome-associated bovine serum albumin (LSM-BSA), showed a significantly higher BSA-specific plaque-forming cell (PFC) response than did mice injected with fluid BSA (fBSA). Physical association between the liposome carrier and the protein antigen is imperative for potentiating the PFC response, since the injection of empty liposomes, together with fBSA, was found to be ineffective in inducing an immune response. Liposome-associated protein antigen was found to be a potent stimulator of immunological memory, as demonstrated by the ability of LSM-BSA primed animals to generate a vigorous PFC response upon challenge with the weakly immunogenic fBSA. The injection of congenitally athymic homozygous nude (Nu/Nu) mice with LSM-BSA failed to induce significant antibody formation, whereas the heterozygous (Nu/+) littermates gave a normal PFC response to the same LSM-BSA preparation. Thus, BSA remains a T-cell-dependent antigen, despite its entrapment within liposomes, and T lymphocytes appear to play an obligatory role in providing synergistic interactions for eliciting a BSA-specific PFC response to the LSM-BSA.     

Lipopolysaccharide-induced autoantibody response. II. Age-related change in plaque-forming cell response to bromelain-treated syngeneic erythrocytes

In spleen of normal mice, there are relatively large numbers of plaque-forming cells (PFC) against syngeneic or allogeneic red blood cells treated with bromelain (Br. MRBC) and the numbers of PFC remarkably increase by the injection of bacterial lipopolysaccharide (LPS). In this report, age-related change in the anti-Br. MRBC PFC response was studied in vivo and in vitro. It was revealed that mean numbers of splenic anti-Br. MRBC PFC increased in both untreated and LPS-injected mice with age (3--14 months). The increase in anti-Br.MRBC PFC detected in LPS-stimulated spleen was dependent on the numbers of PFC in untreated spleen, but not related to the numbers of anti-TNP PFC nor the degree of 3H-thymidine incorporation assessed in in vitro culture. These results imply that enhanced anti-Br.MRBC PFC response was not merely due to polyclonal activation of B lymphocytes. Reasons for increased PFC numbers were analyzed in special references to suppressor activities. The experimental results were obtained suggesting that suppressors were not involved in anti-Br.MRBC PFC response. There were also no marked differences in the acceptability of suppressive signals between young and older spleen cells. It was concluded that hightened anti-Br.MRBC PFC response in older mice might be due to spontaneous increase in the size of Br.MRBC-reactive clone.     

Differentiation factors for human specific B cell response

Nonspecific T cell factors produced by lectin-activated human peripheral blood lymphocytes (PBL) were used to restore the T-dependent B cell response to trinitrophenyl-polyacrylamide (TNP-PAA). Preincubation experiments with the particulate antigen TNP-PAA and/or a soluble TNP-protein conjugate show that a first specific signal provided by the antigen and nonspecific lymphokines sequentially acts on B cells. By gel filtration the T cell-replacing factor (TRF) activity is present in the 30-15-kDa fraction of T cell supernatants and is associated to interleukin 2 (IL2). However, absorption of IL2 does not abolish the TRF activity. Moreover, chromatofocusing of this 30-15-kDa material allows the obtaining of an IL2-free fraction containing a differentiation factor (with an isoelectric point of 5.7 +/- 0.2). The ability of this fraction to restore the anti-TNP response is manifest in the presence of a 50-kDa B cell growth factor. This latter, prepared by a combination of absorption on concanavalin A-Sepharose and gel filtration, was IL2 free and unable to support the anti-TNP response. We thus directly demonstrate that in the absence of IL2 three separate signals (the antigen, T cell-derived growth and differentiation factors) are involved in human-specific B cell response.     

Primary in vitro plaque-forming cell response to DAGG-Ficoll: LPS-induced enhancement mediated by interleukin-1.

The specific primary in vitro plaque-forming cell (PFC) response of C57B1/6 nu/nu spleen cells to the Type 2 T-independent (TI-2) antigen DAGG-Ficoll was analysed in the absence of T cell help in a serum-free medium. Lipopolysaccharide (LPS) enhancement of the antigen-specific response was shown to be mediated by soluble factors contained in the supernatants of LPS-induced bone marrow-derived macrophages. The activity of these supernatants was not associated with residual LPS, since the antigen-specific response of B cells from mice genetically deficient in LPS receptors was equally well enhanced. The activity of these supernatants was associated with interleukin-1 (IL-1) and partially purified IL-1 prepared from P388D1 cells also enhanced the primary in vitro response to DAGG-Ficoll. Limiting dilution analysis experiments showed that only in the presence of exogenously added IL-1 could a single cell type, presumably the B cells, be shown to be limiting.     

Regulation of the immune response. V. Antibody-mediated inhibition of T and B cell cooperation in the in vitro response to red cell antigens

The investigation of the mechanism by which antibody inhibits the production of antibody has been continued using the in vitro response of mouse spleen cells to red cell antigens as assay system. Extending earlier findings demonstrating that antibody does not inhibit (1) the priming of T cells (as opposed to B cells) and (2) the production of antibody by antigen-sensitive B cells, we show here that antibody (endogenous as well as exogenous) does not affect the potential of primed T cells to perform a helper function either. It appears that antibody interferes with the realization of this potential, i. e. the cooperation of T and B cells. Possible mechanisms are discussed, drawing particular attention to the fact that an intact Fc portion is required for antibody to be suppressive in this system.     

Genetic defect in responsiveness to the B cell mitogen lipopolysaccharide.

Splenic B cells C57BL/10ScCr mice fail to respond to the mitogenic principle of lipopolysaccharide (LPS), and do not express a serologically defined "LPS receptor". In contrast, polyclonal B cell responses to both purified protein derivative of tuberculin and lipoprotein are conserved.     

Regulation of B cell immunoglobulin secretion by functional subsets of T lymphocytes in man

Two distinct immunoregulatory T cell subsets, termed T4⁺ and T5⁺, have been defined in man by monoclonal antibodies. Prior studies have shown that the T4⁺ T cell population provided help for B cell immunoglobulin (Ig) production and was required for generation of T5⁺ cytotoxic effector cells. In the present study, the regulatory effects of the T5⁺ T cell subset on B cell Ig secretion were determined in a pokeweed mitogen-driven system. It was found that the T5⁺ subset, in contrast to the T4⁺ subset, was incapable of providing help to B cells and, more importantly, could suppress Ig secretion by B cells in the presence of T4⁺ inducer T cells. Given earlier studies demonstrating that the T5⁺ T cell subset suppressed T cell responses as well, this population appears to represent the major suppressor subset in man for T-T and T-B interactions.     

LPS-induced enhancement of plaque-forming cell response to bromelain-treated syngeneic erythrocytes in mouse peritoneal cell cultures

The effect of bacterial lipopolysaccharide (LPS) on the development of plaque-forming cells (PFC) against bromelain-treated syngeneic mouse red blood cells (Br-MRBC) was studied in peritoneal cell (PC) cultures. It was found that LPS enhances the development of PFC to Br-MRBC and increases DNA synthesis in PC cultures. The LPS-induced enhancement of PFC to Br-MRBC, however, does not appear to require cell proliferation, since it also occurred in PC cultures pretreated with mitomycin C. In addition, the LPS-induced B lymphocytes blastogenesis is under the control of macrophages, while cell differentiation of precursor B lymphocytes into cells actively producing antibodies against Br-MRBC is regulated by suppressor T lymphocytes.     

Regulation of the T cell response

The T cell branch of the immune system can respond to a virtually infinite variety of exogenous antigens, thus including the possibility of self-antigen recognition and dangerous autoimmune reactions. Therefore, regulatory mechanisms operate both during ontogeny within the thymus and after birth in the periphery. The control of self-reactive T cells occurs through a process of negative selection that results in apoptosis of T cells showing high affinity for self-peptides expressed at the thymic level by means of promiscuous gene expression. Self-reactive T cells escaped to negative selection are controlled in the periphery by other regulatory mechanisms, the most important being natural Foxp3+ T regulatory (Treg) cells. Regulation is also required to control excessive effector T cell responses against exogenous antigens, when they become dangerous for the body. Three types of effector T cells have been recognized: T helper 1 (Th1) cells, which are protective against intracellular bacteria; Th2 cells, which play some role in the protection against nematodes, but are responsible for allergic reactions; Th17 cells, which are probably effective in the protection against extracellular bacteria, but also play a role in the amplification of autoimmune disorders. Abnormal or excessive Th effector responses are regulated by different mechanisms. Redirection or immune deviation of Th1- or Th2-dominated responses is provided by cytokines [interferon-gamma (IFN-gamma) vs. interleukin-4 (IL-4)] produced by the same cell types and by the CXCR3-binding chemokines CXCL4 and CXCL10. Moreover, both Th1 and Th2 responses can be suppressed by adaptive Treg cells through contact-dependent mechanisms and/or the production of IL-10 and transforming growth factor-beta (TGF-beta). Finally, TGF-beta1 can promote the development of both Th17 effector and adaptive Treg cells, while the contemporaneous production of IL-6 contributes to the development of Th17 cells, but inhibits Treg cells. The development of Th17 cells is also down-regulated by IL-4 produced by Th2 cells and by IFN-gamma produced by Th1 cells.     

Dietary restraint and responsiveness to sensory-based food cues as measured by cephalic phase salivation and sensory specific satiety.

Responsiveness to sensory-based food cues was examined in restrained and unrestrained, normal-weight subjects identified with the Three-Factor Eating Questionnaire. Salivary flow rate was measured with no food present and while subjects viewed hot pizza. In the presence of food, restrained eaters had a mean salivary flow rate (0.388 g/min) greater than twice that of the unrestrained eaters (0.186 g/min). During sensory specific satiety testing, subjects tasted and rated the pleasantness of 9 foods, then received a meal of either cheese and crackers or cookies. Changes in pleasantness for the tasted foods were evaluated at 2, 20, and 40 min following the meal. Both restrained and unrestrained subjects displayed similar patterns of sensory specific satiety, i.e., the pleasantness foods which were eaten decreased relative to foods tasted but not eaten. These patterns were unaffected by the type of food consumed in the test meal. These data demonstrate that restrained eaters show moderately enhanced salivary responses but no changes in sensory-specific satiety to food stimuli, suggesting that heightened responsiveness to the sensory properties of foods may not be a generalized phenomenon in restrained eaters.     

Depression of direct plaque-forming cell response in mouse spleen cell cultures by aggregated IgG2b-induced factors

Mouse spleen cells were treated with concanavalin A (Con A) or aggregated mouse IgG2b for 48 h in culture. When cells thus treated were added to fresh mouse spleen cell cultures immunized with SRBC they depressed the response of B lymphocytes as measured by enumerating plaque forming cells (PFC) on the fourth day of culture.When supernatant from cells cultured with IgG2b was added to immunized cultures this resulted in depression of PFC generation similar to that observed by addition of treated cells. The depression observed was essentially in the same range as that observed by addition of Con A treated cells or their supernatant.These observations extend previous work suggesting that IgG2b-induced PFC depression may result from activation of suppressor T cells with elaboration of soluble suppressor factors. This mechanism of immunomodulation may be important in the pathogenesis of immune complex disorders.     

Characterization of human T suppressor-inducer, -precursor and -effector lymphocytes in the antigen-specific plaque-forming cell response

Suppression of an antigen-specific plaque-forming cell response of human blood lymphocytes can be effected by T mu+ cells that have been primed previously by antigen in vitro for 6 days. While lacking the capacity to suppress the plaque-forming response directly, these primed T mu+ suppressor-inducer cells stimulate a subpopulation of unprimed T mu gamma- cells to differentiate to T gamma + suppressor-effector cells. The T mu+, T gamma+ and T mu gamma- subsets have been shown to be heterogeneous populations of cells. Therefore, the functionally defined T suppressor-inducer, -precursor and -effector cells were characterized by OKT monoclonal antibodies and by the capacity to form rosettes with autologous erythrocytes (ar+). Evidence will be presented that in vitro a T4+mu+ar- cell induces a T8+mu gamma-ar+ precursor cell to differentiate to a T8+gamma+ar- suppressor-effector cell. A similar T suppressor-effector cell can also be isolated directly from peripheral blood of normal donors.     

Regulation in man × man somatic cell hybrids: possible negative control of Arylsulphatase A

Quantitative assays demonstrate that the level of the lysosomal enzyme arylsulphatase A (ASA) is very low in the heteroploid human line D98 AH₂. Intraspecific cell fusion between that strain and human diploid fibroblastic strains has been obtained. Hybrid cells are distinguished by their karyotypes and by the electrophoresis pattern for phosphoglucomutase, locus PGM₁. ASA activity of hybrid cells was nearly as low as activity of the D98 AH₂ line: deficiency is dominant over non deficiency. Several hypotheses are discussed: one of them involves a negative control of the enzyme arylsulphatase A.     

Cytomegalovirus-specific CD4 T-cell and glycoprotein B specific antibody response in recipients of allogenic stem cell transplantation.

BACKGROUND: The human cytomegalovirus (HCMV) causes severe complications in immunosuppressed patients, resulting in increased morbidity and mortality. The immunological components important for the control of HCMV are still not completely understood. OBJECTIVE AND STUDY DESIGN: To evaluate the importance of cellular and humoral immunity in stem cell transplant (SCT) recipients, we analysed levels of HCMV specific IFN-gamma producing CD4+ cells and glycoprotein B (gB) specific antibodies in HCMV positive SCT patients with and without reactivation episodes after SCT. RESULTS AND CONCLUSION: Patients without HCMV reactivation episodes showed a slow but steady increase in both parameters after SCT, indicating that initial high levels of gB specific antibodies or HCMV specific CD4+ IFN-gamma+ cells are not necessary to prevent reactivation of HCMV. In contrast, patients with reactivation episodes showed a steep, significant increase in HCMV specific CD4+ IFN-gamma+ counts just prior to HCMV reactivation, followed by a decline after the reactivation period. Patients who underwent only a single reactivation generated significant higher amounts of CD4+ IFN-gamma+ cells, than did patients with further reactivation episodes. The course of gB specific antibodies for reactivating patients was different, with significantly higher average values in the patients with HCMV reactivation. This indicates that patients with a HCMV reactivation exhibit a stronger humoral dominated immune response.     

Regulation of the immune response in Plasmodium falciparum malaria. II. Antigen specific proliferative responses in vitro.

The antigen-induced DNA synthesis in vitro in lymphocytes from patients with acute Plasmodium falciparum malaria was investigated. The patients and healthy controls from Sweden or Colombia were the same as those studied in the accompanying paper (Troye-Blomberg et al., 1983). The malarial antigens used were sonicated membrane preparations or purified and concentrated supernatants from in vitro cultures of P. falciparum; similar preparations derived from normal human erythrocytes served as control antigen. In the patients' lymphocytes P. falciparum antigens induced a weak or moderate but significant stimulation of DNA synthesis, peaking after 3-4 days of incubation. This early response was specific for P. falciparum since it was not obtained with lymphocytes from healthy donors nor with those from patients with acute P. vivax or P. ovale malaria. No antigen-induced response was seen in about half of the P. falciparum patients. However in a few negative cases, available for consecutive testing, positive reactions were seen with lymphocytes taken 2 weeks after infection when the blood of these patients was free of parasites. The early response induced in patients' lymphocytes to the P. falciparum antigens was not obtained with RBC antigen. However, these preparations frequently induced a response rising to significant levels later during incubation (day 5-6). Similar delayed responses were obtained when either patients' or control donors' lymphocytes were exposed to the P. falciparum antigens. This indicates that both the RBC and the parasite preparations contained mitogenic substances affecting human lymphocytes in general and easily obscuring the P. falciparum specific response seen only in the patients. This latter response was relatively low and short lived, suggesting that it reflected a secondary in vitro stimulation of in vivo primed lymphocytes and that it was regulated by suppressor mechanisms.     

Chronic restraint stress induces severe disruption of the T-cell specific response to tetanus toxin vaccine

Chronic stress is known to induce immunological disorders. In the present study we examined the consequences of chronic restraint stress on the immune response to tetanus toxin in mice. We investigated the repartition of subsets of lymphoid cells in blood and spleen, the functional ability of lymphocytes to proliferate and to produce cytokines, and antibody titres against tetanus toxin following stress. We report discordance of the stimulation index of lymphocytes in the restraint group: the proliferating rate severely decreased following stimulation with a relevant antigen, whereas it increased with mitogen. Thus, we report a decrease in cytokine production with relevant antigen (interferon-gamma and interleukin-10), without a T helper type 1 and 2 secretion imbalance. Moreover, we observed an alteration in the humoral response, including a delay in isotype maturation and an immunoglobulin G1/G2a imbalance.     

CD5 (Ly-1)-negative, conventional splenic B cells make a substantial contribution to the bromelain plaque-forming cell response in CBA and BW mice.

CD5 (Ly-1) B cells are a minor subpopulation in mouse spleen and are thought to be responsible for the production of natural autoantibodies to bromelain-treated autologous erythrocytes (Br-RBC). Here it is shown that substantial numbers of conventional, CD5-negative, splenic B cells also secrete these antibodies in CBA and (NZB x NZW)F1 mice, whereas in NZB and BALB/c mice they are all produced by the CD5 B-cell population. However, stimulation with bacterial lipopolysaccharide in vivo preferentially activates the CD5 B-cell group to anti-Br-RBC antibody secretion.     

Regulation of immune response by T cell co-signaling. ]

The activation of naive T cells requires two signals from the antigen presenting cells (APC). Firstly, an antigen specific signal which is triggered by the binding of the T cell receptor (TCR) to the peptide-MHC complex, and secondly, antigen nonspecific signals initiated through a set of co-signalling receptors. Co-signalling molecules are cell-surface glycoproteins that play essential roles for the communication of a T cell with virtually all other host cells by modulating and fine-tuning TCR signals. On the basis of their functional outcome, co-signalling molecules can be divided into co-stimulators and co-inhibitors, which promote or suppress T-cell activation, respectively. By expression at the appropriate time and location, co-signalling molecules positively and negatively control the priming, growth, differentiation and functional maturation of a T-cell response. In this article, I overview property of co-signaling molecules in the CD28- and TNFR family and discuss their potential functional relationships with each other. In addition, role of these co-signalling molecules in various diseases, such as autoimmune diseases, graft rejection, allergy, inflammatory bowel disease, and cancer, and the therapeutic potential of targeting these molecules to enhance or curtail an ongoing immune response in these diseases are discussed.