Feedback inhibition of specifically sensitized lymphocytes

Validation of a Candida albicans delayed-type hypersensitivity (DTH) model in female juvenile rats for use in immunotoxicity assessments

Establishing an in vivo cell-mediated immunity (CMI) assay, such as the delayed-type hypersensitivity (DTH) assay, has been identified as an important gap and recommended to receive highest priority for new model development in several workshops on developmental immunotoxicity. A Candida albicans DTH model has recently been developed that has the advantage over other DTH models, which use alternative sensitizing antigens, in that antigen-specific antibodies, which may interfere with the assay, are not produced. In addition, the in vivo C. albicans DTH model was demonstrated to be more sensitive in detecting immunosuppression than DTH models using keyhole limpet hemocyanin (KLH) or sheep red blood cells as antigens, as well as some ex vivo CMI assays. While KLH and sheep red blood cells are non-physiological immunogens, C. albicans is an important human pathogen. The present studies were conducted in order to optimize and validate the C. albicans DTH model for use in developmental immunotoxicity studies using juvenile rats. Three known immunosuppressive compounds with different mechanisms of action were tested in this model, cyclosprorin A (CsA), cyclophosphamide (CPS), and dexamethasone (DEX). Animals were sensitized with formalin-fixed C. albicans on postnatal day (PND) 28 and challenged with chitosan on PND 38. Drug was administered beginning on PND 23 and continued until PND 37. Exposure to each of the three immunotoxicants resulted in statistically significant decreases in the DTH response to C. albicans-derived chitosan. Decreases in footpad swelling were observed at ≥10 mg CsA/kg/day, ≥5 mg CPS/kg/day, and ≥0.03 mg DEX/kg/day. These results demonstrate that the C. albicans DTH model, optimized for use in juvenile rats, can be used to identify immunotoxic compounds, and fills the need for a sensitive in vivo CMI model for assessments of developmental immunotoxicity. Abbreviations Ab, antibody APC, antigen presenting cell BSA, bovine serum albumin C. albicans, Candida albicans CI, challenge interval CMI, cell-mediated immunity CO, challenge only CPS, cyclophosphamide CsA, cyclosporin A CTL, cytotoxic T lymphocyte DEX, dexamethasone DIT, developmental immunotoxicity DTH, delayed-type hypersensitivity ip, intraperitoneal KLH, keyhole limpet hemocyanin MLR, mixed lymphocyte reaction OVA, ovalbumin PBS, phosphate-buffered saline PND, postnatal day sc, subcutaneous SEM, standard error of the mean SRBC, sheep red blood cells.

Validation of the Candida albicans delayed-type hypersensitivity (DTH) model in the female B₆C₃F₁ mouse for use in immunotoxicological investigations

Although numerous models are used to evaluate the immunotoxic effects of xenobiotics on cell-mediated immunity (CMI), no holistic model for evaluating such effects on the delayed-type hypersensitivity (DTH) response has gained widespread acceptance. Due to a lack of interference from antigen-specific antibody production, the Candida albicans DTH model has recently been demonstrated to be a more appropriate model for assessing effects on CMI than other DTH models that utilize different sensitizing antigens, such as sheep erythrocytes (SRBC) or keyhole limpet hemocyanin (KLH). The present studies were conducted to validate the C. albicans DTH model for its ability to detect suppression (or the lack thereof) of CMI following exposure for 28 days to well-characterized immunosuppressive drugs, each having a different mechanism of action. The compounds evaluated included azathioprine (AZA), cyclophosphamide (CPS), cyclosporin A (CSA), dexamethasone (DEX), and the non-immunotoxic compound, benzo[e]pyrene (B[e]P). Exposure to each of the four known immunotoxicants resulted in statistically significant decreases in the DTH response to C. albicans. Footpad swelling was decreased following exposure to AZA at ≥ 20 mg/kg but not at 10 mg/kg, CPS at ≥ 10 mg/kg but not at 5 mg/kg, CSA at ≥ 3 mg/kg but not at 1 mg/kg, or DEX at ≥ 0.3 mg/kg (intermittently at 0.1 mg/kg) but not at 0.03 mg/kg. As expected, exposure to B[e]P for 28 days at doses up to 40 mg/kg had no effect on the DTH response. These results demonstrated that the C. albicans DTH assay in the B₆C₃F₁ mouse was capable of appropriately classifying each test article as to its immunotoxic effects on CMI. Furthermore, comparisons of these results with previous reports of effects on ex vivo CMI end points suggest that this DTH assay may be more sensitive than standard ex vivo assays at detecting immunosuppressive effects.

Establishment and comparison of delayed-type hypersensitivity models in the B₆C₃F₁ mouse

The objective of these studies was to establish and compare delayed-type hypersensitivity (DTH) models, using keyhole limpet hemocyanin (KLH), sheep red blood cells (SRBC), and Candida albicans as sensitizing antigens, for their capability to assess a DTH response (utilizing footpad swelling as the endpoint) with minimal confounding factors resulting from antigen-specific antibody (Ab) production. The key elements of the DTH are the sensitization dose, time interval between sensitization and challenge [i.e. the challenge interval (CI)], and the challenge dose. Models were established by first determining the challenge dose, or the amount of antigen that produced no greater footpad swelling 24-h post-injection than the trauma induced by injection of physiological saline. Time-course studies determined the CI that produced a peak response for each antigen. Dose-response sensitization studies were conducted to determine the optimum sensitization concentration (i.e. maximum footpad swelling with minimal impact by antigen-specific Ab production). Footpad swelling decreased dose-responsively with increasing KLH sensitization concentration and corresponded to a dose-responsive increase in KLH-specific Ab levels. In the SRBC model, footpad swelling decreased at the high dose (1 x 10⁹ SRBC/mouse), and a corresponding increase in SRBC-specific Ab was observed at this dose level. A dose-responsive increase in footpad swelling was observed in the C. albicans model up to 3 x 10⁷ organisms/mouse, while antigen-specific antibody levels were not different from background (unsensitized) levels following sensitization with any concentration of C. albicans (up to 1.2 x 10⁸ organisms/mouse, the highest concentration tested). Finally, each model was evaluated for its ability to detect immunosuppression following exposure to benzo[a]pyrene (B[a]P), with the C. albicans model demonstrating greater sensitivity than the other models. These results indicate that, of the three models examined here, the C. albicans DTH model may be the most appropriate model for evaluating effects on cell-mediated immunity when conducting immunotoxicological investigations.

Different immune correlates associated with tumor progression and regression: implications for prevention and treatment of cancer

Observations show that humans and animals respond immunologically to most cancers. Why does the immune system then fail to control cancer? We argue from the literature that there is a commonality in the regulation of responses against most murine tumors, and that a major mechanism of escape may be deviation of an effective Th1, cytotoxic T lymphocyte response to a less effective response with a Th2 component. We examined this hypothesis with two well-studied murine tumors. We found, following primary tumor implantation, that resistance correlates with Th1 responses and IgG2a antibody production and progression with mixed Th1/Th2 responses and production of IgG1 and IgG2a antibodies. Resistance is associated with a modulation of the anti-tumor response towards the Th1 pole in both systems. We conclude that the immune responses against these two tumors are in accord with our hypothesis, and argue that this is likely to be true of many human and murine tumors. The correlation of IgG isotype of anti-tumor antibody with the Th1/Th2 nature of the anti-tumor response readily allows one to longitudinally monitor the changing nature of the anti-tumor response. We suggest that such monitoring can guide immunotherapy to maximize the effectiveness of the host's immune response against cancer.

Nonoverlapping expression of IL10, IL12p40, and IFNgamma mRNA in the marginal zone and T cell zone of the spleen after antigenic stimulation

The differentiation of CD4(+) T cells is regulated by cytokines locally within the compartments of secondary lymphoid organs during adaptive immune responses. Quantitative data about the expression of cytokine mRNAs within the T and B cell zones of lymphoid organs are lacking. In this study, we assessed the expression of multiple cytokine genes within the lymphoid compartments of the spleen of rats after two types of stimulation. First, the spleen was stimulated directly by a blood-derived Ag. Second, the spleen was stimulated indirectly by incoming lymphocytes that had been activated and released during a proceeding immune response at a distant tissue site. Using laser microdissection, we show that the expression of cytokine mRNAs was compartment specific, transient, and preceded cell proliferation after the direct antigenic stimulation. Surprisingly, the indirect stimulation by incoming activated lymphocytes induced similar cytokines in the T cell zone. However, the nonoverlapping expression was lost and IL10 appeared as the major cytokine in all compartments. Thus, tracking two types of immune activation without disturbing the integrity of structures reveals distinct and overlapping events in the compartments of the spleen. This information adds a new dimension to the understanding of immune responses in vivo.

Splenic B cells are required for tolerogenic antigen presentation in the induction of anterior chamber-associated immune deviation (ACAID)

Ocular immune privilege is the result of a number of protective mechanisms, including a specialized immune response to antigen encountered in the anterior chamber of the eye. Anterior chamber-associated immune deviation, or ACAID, is characterized by the antigen-specific, selective down-regulation of systemic cell-mediated and humoral immune responses. One current hypothesis of the initiation of ACAID predicts that ocular APC process antigen and then migrate out of the eye and to the spleen where various regulatory T-cell populations are generated. A novel in vitro model of the ACAID spleen was developed to study the cells involved in the generation of suppressed T-cell immunity. ACAID APC co-cultured with whole splenocytes or splenic B and T cells induced efferent suppressors of delayed-type hypersensitivity (DTH). However, ACAID APC co-cultured with splenic T cells did not generate efferent suppressors of DTH. The requirement for B cells was confirmed with B-cell knockout mice. ACAID APC co-cultured with splenocytes from B-cell knockout mice did not induce efferent suppressors of DTH. Moreover, ACAID could not be induced in B-cell knockout mice in vivo. The reconstitution of B-cell knockout mice with wild-type B cells restored ACAID. In summary, these data confirm the role for B cells in the splenic phase of ACAID. A putative mechanism predicts that ACAID APC release antigenic peptides to B cells in the spleen. B cells then present antigen in a tolerogenic manner leading to the generation of regulatory T cells.

Age-related decline in humoral immunity caused by the selective loss of TH cells and decline in cellular immunity caused by the impaired migration of inflammatory cells without a loss of TDTH cells in SAMP1 mice

We investigated the cellular basis of the age-related decline in antibody (Ab) and delayed-type hypersensitivity (DTH) responses to sheep red blood cells (SRBC) in vivo in short-lived senescence-accelerated mouse (SAM) P1. In SAMP1 mice, age-related decreases in CD4+ T cells in the peripheral blood occurred earlier than in control mice and occurred in parallel with the age-related decline in Ab and DTH responses. In addition, the involution of the thymus was faster. The injection of thymic T cells from young mice before sensitization completely restored the Ab responses in aged SAMP1 mice. These data suggest that the age-related decline in Ab response is due to the age-related early loss of helper-T (TH) cells. On the other hand, the local transfer of spleen cells from sensitized aged donors into the footpads of naive syngeneic recipients evoked strong DTH responses, demonstrating the existence of DTH-mediating T (TDTH) cells in the spleens of aged SAMP1 mice. Moreover, the local injection of naive spleen cells from young donors, together with the antigen, into the footpads caused DTH responses in sensitized aged recipients. These findings indicate that TDTH cells were induced and were able to migrate and function as effector cells in aged mice. When naive spleen cells from aged donors were injected locally into the footpad, they restored the DTH response in aged mice, but this effect did not work if the cells were injected intravenously. This demonstrates that the inflammatory cells of the aged mice were able to work at the local site, but could not migrate there. The intravenous injection of naive spleen cells from young donors restored the DTH response in aged mice, suggesting that the endothelial cells of aged mice were not impaired and permitted the inflammatory cells to migrate into the extravascular tissues. Thus, although the age-related decline of the Ab and DTH responses occur in parallel, we found different effects of aging on TH and TDTH cells in SAMP1 mice. Furthermore, our data suggest that the reason for the low DTH response in aged SAMP1 mice is not the loss of TDTH cells, but rather the impaired migration of inflammatory cells into the local site.

The role of antigen-presenting cells in the regulation of delayed-type hypersensitivity. I. Spleen dendritic cells

A previously unreported mechanism for the induction of delayed-type hypersensitivity (DTH) was studied in detail. The subcutaneous injection (without adjuvant) of spleen dendritic cells (DC) pulsed with keyhole limpet haemocyanin (KLH) into syngeneic BALB/c mice caused DTH when the ear was later injected with the same antigen. When KLH-pulsed DC were transferred intravenously, DTH was not induced, although the titre of anti-KLH antibodies rose after such transfer. The intravenous transfer of KLH-pulsed DC into mice immunized subcutaneously with KLH in complete Freund's adjuvant (CFA) at the same time (in the sensitization phase), but not when the ear was challenged with KLH (in the effector phase), had a suppressive effect on DTH, in an H-2-restricted way. When radiolabelled DC were transferred intravenously, they migrated into the spleen, but when transferred by subcutaneous injection, they stayed in the skin or migrated into the lymph nodes. In splenectomized mice immunized with KLH, the intravenous transfer of KLH-pulsed DC did not cause production of anti-KLH antibodies and did not suppress DTH. These findings suggest that the anatomical sites in which antigens are presented (i.e. the spleen or lymph nodes) rather than the type of cell that first presents antigens to the immune system governs whether DTH or antibody production is induced. Antibody production was induced when antigens were presented in the spleen.

Interleukin 6 inhibits delayed-type hypersensitivity and the development of adjuvant arthritis

We studied the effect of interleukin 6 (IL 6) on the delayed-type hypersensitivity (DTH). In mice immunized with sheep red blood cells (SRBC), a DTH response was evoked by antigen challenge into the hind paw 5 days after immunization. The magnitude of the response was assessed by footpad swelling measured 24 h after antigen challenge. IL 6 significantly suppressed the DTH in its induction phase in a dose-dependent manner when administered s.c. into the back at a dose of greater than 2.5 micrograms twice a day (5 micrograms/day) for 5 consecutive days from the day of immunization (day 0) to 1 day before antigen challenge (day 4). Heat-inactivated IL 6 did not suppress the DTH response. Furthermore, the suppressive activity of IL 6 was completely abolished by affinity chromatography on an anti-IL 6 antibody. This suppression was also obtained when IL 6 was administered only on day 0 and day 1, but not on days 3 and 4. This indicates that IL 6 acts on the early part of the induction phase of DTH development. Furthermore, footpad swelling was suppressed even by the administration of IL 6 after antigen challenge. These results show that IL 6 suppresses both the induction and effector phases of DTH. To confirm further this inhibitory effect of IL 6, we examined its effect on the development of adjuvant arthritis in rats. Administration of IL 6 also significantly suppressed the development of adjuvant arthritis.

Delayed-type hypersensitivity and protection in mice following immunization with Plasmodium berghei sporozoites

The measurement of footpad swelling (FPS) following the inoculation of sporozoite antigen (Ag) into the hind footpad (HFP) of outbred mice was used as an in vivo test of delayed-type hypersensitivity (DTH) to attenuated sporozoite immunization. An attempt was made to correlate DTH with protective antisporozoite immunity. The optimum time for testing DTH following a single intravenous immunization was four days. The optimum sensitizing dose was 1 x 10(5) attenuated sporozoites. A single immunization gave a greater FPS than multiple immunizations. Mice immunized with irradiation-attenuated sporozoites could be protected from a lethal challenge with nonattenuated sporozoites. The FPS response to mosquito debris Ag was minimal in mice sensitized by bites from infected mosquitos. Nude mice failed to develop an FPS response and could not mount a protective immunity with attenuated sporozoites. However, splenectomized mice did have an FPS response following sensitization. Mice infected with blood-stage parasites had negligible FPS response to sporozoite Ag. The FPS response to sporozoite Ag proved to be a correlate of DTH in mice sensitized with sporozoites.

Altered immune response (humoral and delayed-type hypersensitivity reactions) to sheep red blood cells in the course of experimental filarial infections (Litomosoides carinii, Brugia malayi, Acanthocheilonema viteae) of Mastomys natalensis

Litomosoides carinii-, Acanthocheilonema viteae- or Brugia malayi-infected Mastomys natalensis were sensitised against sheep red blood cells (SRBC) on various occasions after infection to determine the effect of filarial infections on the immune response to a non-filarial antigen. The phagocytic activity of the reticuloendothelial system (RES) was controlled in vivo by the elimination of 51Cr-labelled SRBC. Antibody titres against SRBC (agglutinating and lytic antibodies) were similar to those of uninfected controls in L. carinii- or B. malayi-infected Mastomys sensitised during prepatency or early patency up to 90 days post infection (p.i.) but were reduced in animals sensitised during patency. A significant inverse correlation existed between anti-SRBC antibody titres and microfilaraemia levels. In contrast, A. viteae-infected Mastomys showed reduced humoral anti-SRBC responses at the end of prepatency, whereas the response tended towards normal with increasing parasitaemia. Delayed-type hypersensitivity (DTH) against SRBC was measured as footpad swelling after sensitisation by the s.c. or i.v. route and intraplantar challenge. DTH reactions were reduced during prepatency in all infections after s.c. sensitisation. During patency, 24-h reactions were similar to those of age-matched controls but the swelling persisted 24 or 48 h longer than in the latter. In A. viteae infections, even enhanced 24-h reactions were found during patency. Histological investigations did not reveal differences in the type of cell infiltrations between infected and control animals. After i.v. sensitisation with SRBC, L. carinii- and A. viteae-infected animals showed weaker DTH reactions than the controls, independent of the period after infection. In the case of B. malayi infections, DTH reactions were similar to those of controls during early prepatency, whereas reduced DTH responses were observed later than 50 days p.i. As shown in L. carinii-infected animals, depressed DTH reactions after i.v. sensitisation did not depend on an altered expression phase but rather on an altered regulation during the inductive phase of the response: increases in the sensitising SRBC doses that caused decreasing DTH reactions in uninfected animals led to enhanced reactions in infected animals. Phagocytosis of i.v. injected 51Cr-labelled SRBC was enhanced during prepatency in L. carinii infection and during patency in all infections.

Enhancement of the Arthus reaction and suppression of delayed type hypersensitivity (DTH) by pluronic F-68, a detergent frequently used to prepare perfluorocarbon emulsions

The effect of a 20% w/v RM101 (perfluorobutyltetrahydrofuran) emulsion containing 5% w/v of the detergent Pluronic F-68 or 5% w/v Pluronic F-68 given alone on the Arthus reaction and on delayed type hypersensitivity (DTH) were evaluated in female A/J mice. The test substances were administered i.v. at 1% body weight at 0,4,7,14 and 28 days prior to the i.p. immunization with 10(7) sheep red blood cells (SRBC). The increase in footpad swelling at 4 h (Arthus reaction) and at 24 h (DTH) after elicitation with the s.c. administration of 10(8) SRBC into the left footpad was used to assess immune competence. Pluronic F-68 given alone enhanced the Arthus reaction only when administered on day 0 of immunization. Pluronic F-68 given alone, as well as the perfluorocarbon emulsion containing Pluronic F-68, suppressed the 24 h DTH for as long as 4 days prior to immunization. Nonemulsified perfluorocarbon, on the other hand, had no effect on either the Arthus reaction or on DTH. The immunostimulatory agent, levamisole, administered (10 mg/kg i.p.) 1.5-2 h prior to immunization with SRBC counteracted both the Arthus reaction and the DTH response produced by Pluronic F-68. The present data clearly demonstrate that the changes in Arthus reaction and the DTH response are due to the Pluronic F-68 used to emulsify the RM101 perfluorocarbon; the changes induced by the detergent in these two immune parameters probably involve separate mechanisms.

Regulation of immune responses by T suppressor cells and by serum in chronic paracoccidioidomycosis

Regulation of cellular responses was studied during the course of chronic murine disseminated paracoccidioidomycosis. Regulation of peripheral blood lymphocyte (PBL) proliferative responses to concanavalin A (Con A) was studied in vitro by mixing PBL from infected and noninfected mice. PBL from mice infected for 18 weeks had depressed responses to Con A and they depressed the Con A responses of PBL from noninfected mice by 95% when they were mixed in a 1:1 ratio. After treatment of PBL from infected mice with anti-Lyt-2.2 antibody plus complement, the responses to Con A were increased to normal values. The percentage of T-cell subpopulations in PBL from infected mice did not differ significantly from those of normal mice. Immunoregulation of delayed-type hypersensitivity (DTH) responses to antigen by serum from infected animals was studied in mice 1 week after intranasal (i.n.) infection, a time when DTH responses were maximal. DTH responses to antigen 7 days after i.n. infection (10(7) CFU Paracoccidioides brasiliensis) were significantly reduced when 0.5 ml of immune mouse serum (ELISA antibody titer to P. brasiliensis antigens 1:10,240) was given i.v. 1 day before infection (P less than 0.01) or 1 day before skin testing (P less than 0.001). Normal mouse serum did not have this effect. The results indicate that progression of chronic disseminated paracoccidioidomycosis was associated with the development of T-cell suppressor activity for Con A responses of PBL, and that DTH responses to antigen were depressed by the administration of serum with specific high titer antibodies.

Effects of Mycobacterium bovis BCG, bacterial lipopolysaccharide and hydrocortisone on the development of immunity to Plasmodium berghei

Mycobacterium bovis (BCG) aumenta significantemente o desenvolvimento da imunidade nos camundongos CFW, C57BL/6, C57BL/l0ScN e BALB/c (Nu/+) para os estágios eritrocitos do Plasmodium berghei. Camundongos tratados com BCG requerem menos ciclos de infecção com P. berghei e cura pelo Fansidar (pirimetamina + sulfadoxina) para desenvolverem imunidade sólida a este parasita do que os controles. Contudo, os animais que receberam BCG 30 dias antes do início da imunização evidenciaram uma perda precoce da imunidade adquirida para o P. berghei, quando comparado com os animais que receberam BCG 14 dias antes ou que não receberam BCG. Assim, sendo, o BCG aumentada a indução na resposta imune do hospedeiro ao P. berghei no curso de infecções subseqüentes. O tratamento de camundongos CFW, BALB/c e C57BL/6 com lipopolissacarídeo bacteriano ou hidrocortisona faz com que os animais requeiram um número maior de ciclos de infecção e cura para tornarem-se imunes ao P. berghei que os controles. O tratamento dos camundongos C57BL/10ScN com hidrocortisona aboliu completamente a sua habilidade de sobrevida subseqüentes a ciclos de infecção com P. berghei e cura pelo Fansidar.

Cell mediated immunity to liver fluke antigens during experimental Fasciola hepatica infection of cattle

Cell mediated immunity (CMI) to Fasciola hepatica antigens was detected by lymphocyte proliferation and interleukin-2 (IL-2) production tests in cattle during the first 4 weeks following liver fluke infection. From the fifth week of infection onwards peripheral blood lymphocytes were unresponsive to fluke antigens by these in vitro tests. Investigations into the cause of this unresponsiveness found no evidence to suggest a selective loss of the IL-2 producing lymphocyte sub-population or that macrophages were responsible for the suppression or that antigen responsive cells were being sequestered in the spleen and mesenteric lymph nodes. Tests carried out on culture supernatants demonstrated the production during this unresponsive period of factors capable of suppressing in vitro responses to PHA. Although further tests failed to show antigen specific suppressor factors the presence of MHC restricted suppressor factors could not be ruled out. The early and transient appearance of CMI during F. hepatica infection of cattle indicates that delayed type hypersensitivity is unlikely to be important in protective immunity in cattle.

Anti-complementary amines are immunological adjuvants in mice

Complement (C) inactivation by ammonia, ethylenediamine and methylamine in mouse serum was studied in relation to a possible adjuvant effect of the substances in a cell-mediated immune response. The amines caused a dose-dependent depletion of both alternative pathway (AP) and overall C activity in vitro and showed also pronounced adjuvant effects in the delayed type hypersensitivity response of mice to SRBC. A significant correlation between momentary inhibition of AP activity and adjuvanticity was observed (r = 0.9995; P approximately 0.02), suggesting a causative relationship between these two phenomena. Both effects seem to be a direct function of the number of amino-groups per molecule. Since, on the other hand, lysosomotropic activity of amines is known to decrease with the number of amino-residues, our findings exclude an important role of direct phagocyte inhibition in the immuno-adjuvanticity of these compounds. A longer persistence and improved presentation of antigen as indirect result of local C-depletion could account for the immunological adjuvant effects of amines.

Immunoregulation of genetically controlled acquired responses to Leishmania donovani infection in mice: demonstration and characterization of suppressor T cells in noncure mice

On a B10 genetic background, genes in the I region of H-2 influence the development of acquired T-cell mediated immunity to Leishmania donovani infection in mice. In previous studies, noncure in H-2d mice could be abrogated by pretreatments with cyclophosphamide or sublethal irradiation. The prophylactic effect of these pretreatments was consistent with deletion of the precursors of suppressor T cells suppressing T-cell-mediated immune responses. In this study, cell transfer experiments provide direct evidence for the role of suppressor T cells in the noncure response. T-cell-enriched populations isolated from the spleens of B10.D2/n mice infected 30, 61, or 85 days previously reversed the prophylactic effect of sublethal irradiation when injected before infection into B10.D2/n mice that had received 550 rads. B-cell-enriched populations failed to transfer suppression in this manner, and T-cell-enriched populations from the spleens of normal B10.D2/n mice had only a transient effect on liver parasite loads. Transfer of suppression with the T-cell-enriched populations from infected donors was abrogated by pretreatment with anti-Thy-1.2 and anti-Lyt-1.2 antisera plus complement but not by pretreatment with anti-Lyt-2.2 plus complement, indicating that the suppressor T cell involved has an Lyt-1+2- surface phenotype. Results are discussed in relation to the possible mechanism of H-2-linked control.

Cellular immune response to sheep erythrocytes: interrelationship between proliferation of popliteal lymph node cells and footpad swelling

Mice were sensitized with graded doses of sheep erythrocytes by the intravenous or subcutaneous route and challenged for delayed-type hypersensitivity (DTH) at different times thereafter. The DTH response as assessed by footpad swelling (FPS) was compared to the spontaneous proliferative response of the popliteal lymph node cells (PLNC). Proliferation of PLNC was optimal after sensitization regimens resulting in optimal FPS. The same was true for mice sensitized under cyclophosphamide modulation. Proliferation of PLNC induced by SRBC was antigen-specific, although some crossreactivity with horse red blood cells was observed. Proliferation of PLNC could be abrogated by treatment with anti-Thy-1.2 antiserum plus complement demonstrating the T cell nature of proliferating cells. In accordance with published data, FPS of mice presensitized with a high dose of SRBC as well as FPS of recipients of spleen cells from high-dose-sensitized donors was suppressed. In marked contrast, PLNC proliferation was not diminished in these mice. Although proliferation of PLNC did not parallel FPS under all circumstances, it seems to be a correlate of the cellular immune response to SRBC.

Delayed-type hypersensitivity response in mice to Treponema pallidum

C3H/HeJ mice which had been primed with either virulent or killed T. pallidum were studied for in vivo delayed-type hypersensitivity (DTH) responses to T. pallidum following local footpad challenge. Mice sustaining a chronic infection of 5 months duration failed to develop a DTH to treponemal antigens, whereas priming by a single intravenous injection with killed organisms resulted in a significant DTH response in mice when challenged 5 days later. Treatment of mice prior to priming with a single sublethal dose of cyclophosphamide (100 mg/kg body weight) not only failed to potentiate T. pallidum-DTH, but abrogated the response observed in untreated primed animals.

Regulation of contact allergy in the B cell--deficient mouse

We have examined the obligate role of B cells in the regulation of allergic contact dermatitis. Our model is ACD in mice made B cell deficient by the chronic administration from birth of a goat antisera to mouse IgM. The following ACD phenomena are well demonstrated in these mice: (1) acquisition and expression of ACD, (2) spontaneous waning of ACD soon after sensitization, (3) immunological tolerance induced by pretreatment with either parenteral hapten or haptenated spleen cells, (4) immunopotentiation by means of either cyclophosphamide or the local administration of a suspension of killed C. parvum (P. acnes), (5) the flare-up of previous test sites following the local administration of parenteral allergen, and (6) acquisition and expression of photo-ACD. We conclude that B cell participation is not required for these ACD phenomena, although an optional or subsidiary function for B regulatory cells is not excluded.

Effect of stimulation and blockade of mononuclear phagocyte system on the induction of suppressor T cells of delayed footpad reaction to SRBC in mice

The role of mononuclear phagocyte system (MPS) in the induction of suppressor T cells which depress the delayed footpad reaction to sheep erythrocytes (SRBC) was studied in mice in which MPS was blocked or stimulated. Colloidal carbon and diethylstilbestrol were used for blockade and stimulation respectively. Adoptive transfer of suppressor T cells was achieved by spleen cells of mice immunized intraperitoneally with varying doses of SRBC. In nontreated mice, 1 x 10(9) SRBC were required to induce suppressor T cells, while 6 x 10(8) could not induce the suppressor T cells. In MPS-blocked mice, however, even 6 x 10(8) SRBC could induce the suppressor T cells. On the other hand, 3 x 10(10) SRBC were required for the induction of suppressor T cells in MPS-stimulated mice. These results suggest that the activity of macrophages as scavenger cells modulates the subsequent induction of suppressor T cells after immunization with high doses of SRBC.

Mechanisms involved in the antibody-mediated suppression of tuberculin-type delayed hypersensitivity: the effects of antigen concentration on tolerance induction, the ability of antigen-antibody complexes to render tolerant and the effects of toleration on antigen-induced in vitro proliferation

Long-lived tuberculin-type delayed hypersensitivity to chicken conalbumin (CA), as measured by skin-reaction, is inhibited in CAF1 mice by passively administered hyperimmune mouse antiserum to CA. We describe here three new parameters of this inhibition: (1) induction of tolerance is not dependent on the concentration of antigen used to sensitize, even when 3.6-fold more antigen is administered than the tolerizing antibodies can bind; (2) antigen-antibody complexes formed in vitro can inhibit; and (3) although induction rather than reaction is suppressed by antiserum treatment, early stages of sensitization are not inhibited. This is shown by the capacity of inguinal lymph node cells from suppressed mice to proliferate in vitro, in response to antigen, 7 and 14 days after sensitization and antiserum treatment. In fact, this in vitro proliferative response is specifically enhanced in suppressed mice on day 7. These results suggest a complex mechanism of antibody-mediated immunoregulation.

Sex-related differences in the pattern of coxsackievirus B-3-induced immune spleen cell cytotoxicity against virus-infected myofibers

Spleen cells from adult BALB/c mice injected intraperitoneally with purified coxsackievirus B-3 were tested for cytotoxicity against 51Cr-labeled syngeneic infected and uninfected myofibers. Both male and female immune cells were active against uninfected targets; this reactivity was evident by day 3 of infection and persisted throughout the first week. However, we observed marked sex-related differences in immune cell cytotoxicities against infected myofibers. Males exhibited a strong T-lymphocyte response 4 to 7 days after infection. In contrast, females exhibited a weak response, and only infrequently were the immune spleen cells of females significantly more reactive against infected myofibers than against uninfected myofibers. The demonstration of a stronger effector cell response against infected myocardial cells in male mice correlates with the observation that clinical adult coxsackievirus B myocarditis and pericarditis occur predominantly in males.

Peritoneal exudate T lymphocytes with specificity to sheep red blood cells. IV. Fc receptors on specific peritoneal exudate lymphocytes and their role in delayed-type hypersensitivity reactions

In mice, delayed-type hypersensitivity (DTH) to sheep red blood cells (SRBC) is mediated by T cells. Peritoneal exudate T cells (PETLs) from mice optimally sensitized for DTH to SRBC form rosettes when interacted with sensitized sheep red blood cells (EA). The binding of EA to PETLs is mediated by a receptor specific for the Fc portion of the antibody (FcR). Biological activity (mediation of DTH) depends on the unreacted state of PETLs and is lost when the latter are either rosetted with EA or reacted with aggregated IgG. Transfer of EA or aggregated IgG-treated PETLs from mice with DTH to SRBC does not lead to adoptive sensitization of recipients. It is suggested that FcR found on the membrane of T cells mediating DTH play a role in the regulation of the cellular immune response to SRBC.

Effect of route of Mycobacterium bovis BCG administration on induction of suppression of sporozoite immunity in rodent malaria

Intravenous immunization of mice with 16,000, 60Co--gamma-irradiated, attenuated sporozoites produced solid immunity to sporozoite-induced malaria when the mice were challenged 21 days after immunization. In contrast, mice injected by various routes with 10(7) viable units of Mycobacterium bovis (BCG) before immunization with irradiated sporozoites were not completely immune to challenge. The extent of reduced protection against viable sporozoites demonstrated with these animals was dependent upon the injection route mycobacteria. The intravenous administration of BCG induced the greatest degree of suppression, followed by the intraperitoneal and subcutaneous routes. BCG injected intramuscularly before sporozoite immunization did not suppress development of immunity. In contrast, mice injected with BCG after immunization with attenuated sporozoites exhibited a lesser degree of suppression. In these animals, only the intravenous injection of mycobacteria reduced immunity.

Absence of correlation between delayed-type hypersensitivity and protection in experimental systemic candidiasis in immunized mice

We found that in mice which had been immunized intraperitoneally with 2 x 10(8) heat-killed Candida albicans cells there was a striking temporal relationship between resistance to systemic challenge with 10(6) living C. albicans cells and a number of measurable cellular parameters of the host response. These included the emergence of delayed-type hypersensitivity and the development of granulocytosis. Since it had been shown in previous work that granulocytosis was associated with an increase in resistance when nonspecific immunostimulation was used, we performed experiments to induce delayed-type hypersensitivity without any measurable modification of the granulocyte population. Adoptive transfer of delayed-type hypersensitivity with spleen cells from immune and resistant donor mice did not produce any increase in resistance in normal recipients. When separate groups of mice were immunized intraperitoneally or subcutaneously with varying doses of heat-killed C. albicans, we found that doses of less than 10(8) cells did induce significant delayed-type hypersensitivity without any increase in granulocytosis. In such mice, as well as in animals pretreated with immunomodulators before immunization with heat-killed C. albicans, the presence of cell-mediated immunity, as measured by the delayed-type hypersensitivity test, was not associated with an increase in resistance against systemic candidiasis. On the contrary, the results suggested that cell-mediated immunity was associated with an increase in the susceptibility of these mice. The same effect on candidiasis susceptibility was observed when animals were immunized with heat-killed filamentous C. albicans.

Specific unresponsiveness to Corynebacterium parvum as measured by delayed hypersensitivity

In order to induce specific unresponsiveness to C. parvum mice were given seven daily i.v./i.p. injections of a high dose of the vaccine, or were given a single dose i.v. injection of C. parvum followed by an i.p. injection of cyclophosphamide (CY). Mice given the high-dose procedure had a significant level of residual footpad reactivity to C. parvum challenge, but subsequent sensitizing injections did not stimulate delayed hypersensitivity (DH). In contrast, mice given C. parvum and CY did not respond to challenge, and they could not be sensitized to C. parvum. Their unresponsiveness was antigenically specific and was stable for at least six weeks. Antibodies to C. parvum were induced by both pretreatment procedures. This is the first report of the production of mice specifically unable to mount DH to a bacterial immune stimulant.

Kinetics of delayed-type hypersensitivity (DTH) reactions and Ig levels in FCA-induced dysgammaglobulinemic B 12 chickens

Kinetic studies on delayed-type hypersensitivity (DTH) to Freund's complete adjuvant (FCA) have been done in spontaneous dysgammaglobulinemic chickens, which have drastically reduced serum IgG levels and highly elevated IgM and IgA levels - in comparison to chickens with normal immunoglobulin (Ig) levels. For a period of five weeks, serum Ig levels, leukocyte migration inhibition (LMIT), and wattle reaction were examined once a week. In normal chickens, FCA treatment resulted in stimulation of IgG, but did not affect IgM synthesis, whereas in spontaneous dysgammaglobulinemic chickens, FCA stimulated only IgM synthesis. Spontaneous dysgammaglobulinemic chickens could produce LMIT and wattle reactions as well as normal birds. Whereas in normal birds, both types of DTH reactions declined continuously about the third or fourth week, in immunodeficient chickens, further increments of LMIT and wattle reactions up to the fifth week persisted as evidenced by LMIT and wattle reactions even 15 weeks after sensitization. In contrast, only minimal signs of reactivity were seen in normal birds. Spontaneous dysgammaglobulinemic chickens, nearly unable to synthesize IgG even after FCA stimulation in vivo, lack suppressive mechanisms regulating the course of DTH reaction to FCA. The possible B-cell nature of the regulatory cell population is discussed.

Transferable suppression and intrinsic unresponsiveness in delayed-type hypersensitivity to sheep red blood cells of mice: two distinct mechanisms?

In mice rendered unresponsive in DTH by the i.v. infection of 10(9) SRBC, two forms of specific unresponsiveness could be distinguished, referred to as intrinsic unresponsiveness and suppression. Suppression could be transferred by splenic T cells. It was short-lived and sensitive to cyclophosphamide (Cy, 100 mg/kg i.v.) given after sensitization. On the other hand, intrinsic unresponsiveness was not transferable by either serum or spleen cells. It was long-lived and resistant to Cy (200 mg/kg i.v.) given after sensitization. Induction of both transferable suppression and intrinsic unresponsiveness depended on Cy-sensitive (200 mg/kg i.v.) precursors. Since no evidence for clonal deletion could be obtained, it is suggested that unresponsiveness in general is mediated by complex cellular interactions which are readily perturbed in transfer experiments. In this way, cell recipients would end up possessing incomplete regulatory circuits, intact circuits still being present in donor animals.

Lack of correlation between delayed-type hypersensitivity and host resistance to Plasmodium chabaudi infection

C57B1/6J mice immunized with Plasmodium chabaudi antigen plus saponin exhibited strong delayed-type hypersensitivity (DTH) reactions to footpad injections of P. chabaudi antigen. However, when immunized mice were challenged with P. chabaudi parasites, DTH was significantly depressed after 3 days of infection. This DTH depression coincided with a steep rise in the titre of malarial antibody in these immunized challenged mice when compared to unchallenged immunized mice. Serum from mice recovering from P. chabaudi infection depressed DTH levels of immunized mice significantly, but spleen cells from convalescent mice only slightly reduced the DTH levels. These results are discussed with respect to the role of cell-mediated immunity in malaria infections.

Lymphocyte-derived chemotactic factor synthesis in initial genital herpesvirus infection: correlation with lymphocyte transformation

Lymphocyte transformation and production of lymphocyte-derived chemotactic factor in response to herpes simplex virus antigen were studied in 15 patients with initial genital herpes and 10 controls. The patients underwent frequent genital examinations, viral cultures, and weekly immunological studies for a period of 11 weeks. The production of lymphocyte-derived chemotactic factor was maximal in week 1 of the disease and declined to control levels by week 6. In contrast, lymphocyte transformation was lowest in week 1, reached a maximum by week 4, and declined to control levels by week 11. Production of lymphocyte-derived chemotactic factor in week 1 was significantly lower in nine patients who developed signs or symptoms of systemic herpes infection than in six who had localized disease. In addition, a marked but transient decline in the production of this lymphokine was observed in patients at the time of clinical recurrence. Virus-specific lymphocyte transformation correlated inversely with the duration of genital pain and lesions and did not correlate with the presence of systemic signs or symptoms. These findings indicate that during initial genital herpes infection the dynamics of lymphocyte transformation and those of lymphocyte-derived chemotactic factor production are different, and that the generation of this lymphokine is an early component of the cellular immune response in this disease. Furthermore, adequate produce of lymphocyte-derived chemotactic factor may be important in restricting herpes simplex virus to the genital area and preventing disease recurrence.

Inhibition of mitogen-induced lymphokine production by cyclosporin A

The new antilymphocytic agent Cyclosporin A was found to inhibit the production and/or secretion of migration inhibitory factor (MIF) in human lymphocytes stimulated by Concanavalin A. Preincubation for one hour with the compound, followed by 8 hr restoration period of the cells in absence of the drug, resulted in moderate decrease in MIF synthesis and/or release. Cell viability was not affected. The agent was shown not to interfere with MIF action on the macrophage. We conclude that the molecular mechanism of action of Cyclosporin A is based, at least partially, on a blockade of synthesis and/or secretion of lymphokines from immunocompetent cells.

Modulation by malaria infection of the induction of T lymphocyte-dependent delayed-type hypersensitivity and antibody formation to sheep erythrocytes in mice

A profound alteration of the inductive phase of delayed-type hypersensitivity and antibody formation to SRBC was found in malaria infected mice when sensitization with this antigen was performed intravenously at a critical time of the disease, but not after subcutaneous immunization, suggesting a major role for the spleen in the mechanism of immunodepression.

Peritoneal exudate T lymphocytes with specificity to sheep red blood cells. III. High dose of antigen induces suppressor T cells which influence the appearance in exudates of effector T cells for delayed-type hypersensitivity and helper T cells for humoral immune responses

Antisera produced in rabbits against adherent cells of rat alveolar or peritoneal lavage fluid (anti-rat alveolar macrophage sera, ARAMS, or anti-rat peritoneal macrophage sera, ARPMS) were used to detect antigenic differences between alveolar (AM) and peritoneal (PM) macrophages in an indirect membrane immunofluorescence (IMF) test. Of all sera tested, the IMF titres were higher with cells of that population which was used for immunization. These differences were found before and after exhaustive absorptions with insolubilized rat plasma, rat erythrocytes, and non-adherant rat kidney, spleen, thymus and bone marrow cells. The differences were not due to antigens specific for one of the macrophage populations, as demonstrated by cross-adsorption studies with macrophages of different localization. It is assumed that two or more macrophage specific antigenic determinants are present in different density in the two macrophage populations.

Peritoneal exudate T lymphocytes with specificity to sheep red blood cells. II. Inflammatory helper T cells and effector T cells in mice with delayed-type hypersensitivity and in suppressed mice

Peritoneal exudate cells were induced in mice 4 days after immunization with SRBC. A low dose of SRBC (10(6) i.v.) caused T lymphocytes to appear in inflammatory exudates. These cells, not only transferred DTH reactions, but also functioned as helper T cells in antibody production after transfer to syngeneic nu/nu recipient mice. After a high dose of SRBC (10(9) i.v.), very few helper T cells and no DTH transferring T cells were found in inflammatory exudates, although they were present in the spleen. It is postulated that T cells mediating DTH reactions and helper T cells behave similarly as far as those dose dependency of appearance in inflammatory exudates is concerned. A high dose of sensitizing antigen causes retention of helper and effector T cells in the spleen, in this way favouring antibody formation; low doses of antigen allow them to leave the spleen, thus favouring mediation of DTH reactions in the periphery.

Immunological behavior after mycobacterial infection in selected lines of mice with high or low antibody responses

Resistance and susceptibility to mycobacterial infection in the Biozzi high and low lines of mice which were genetically selected for their responses to heterologous erythrocytes have been found to be related to the innate ability of nonimmune macrophages to kill or inhibit the growth of the organisms during the first two weeks after infection and to their ability to mount specific and nonspecific immune responses. High antibody-producer mice were more capable of expressing cell-mediated immune parameters than low antibody-producer mice. A direct relationship was observed between the ability of bacteria (BCG vaccine) to multiply inside the reticuloendothelial system and the development of cell-mediated immunity, as measured by the delayed local reaction at the injection site, the lymphoproliferative response in the draining nodes, the tuberculin delayed-type hypersensitivity, the acquired resistance, and the adjuvant effect after BCG inoculation. In high line mice, apart from the inability of their macrophages to inhibit the early growth of bacteria, their lymphocytes in spleen and thymus were more capable of being stimulated in vitro by varying concentrations of living BCG. The data presented in this report are compatible with the hypothesis that a group of genes segregated in each line during the selective breeding controls the innate microbicidal activity.

Receptor sites for complement and for immune complexes on human nonhemopoietic tumor cells

Tumor cells in primary cultures derived from 11 untreated nonhemopoietic cancer patients were reacted with specifically coated sheep erythrocytes. Rosette formation between tumor and indicator cells was assessed, Eight of the primary cultures reacted positively with both IgG-coated (EAIgG) and with IgM-human complement coated (EAIgMC or EAIgMC 4,3) sheep erythrocytes. EAIgG rosette formation in positive cultures ranged from 25 to 85%, and for EAIgMC/EAIgMC 4,3 reactivity ranged between 22--95%. Rosette formation with E (uncoated) and EAIgM was negligible. These findings suggest that human nonhemopoietic tumor cells may carry on their surface receptor sites for an IgG component of immune complexes and for human complement. These receptor sites may be important in the host-tumor relationship.

Regulatory role of suppressor T cells in the expression of delayed-type hypersensitivity in mice. I. Transient appearance of suppressor T cells for the expression of delayed footpad reaction induced with lipid-conjugated lysozyme

Delayed footpad reaction (FPR) to lysozyme (Lys) in mice was induced without antibody responses by lipid-conjugated lysozyme (D.Lys). This FPR was suppressed by priming s.c. with a high dose (10 mg) of Lys 2 weeks previously (unresponsiveness). Spleen cells from the unresponsive mice suppressed antigen-specifically FPR in mice previously immunized with D.Lys, and also suppressed passive transfer of FPR by D.Lys-immune lymphoid cells into normal mice. The suppressive activity of the spleen cells was abolished by treatment with anti-phi anti-serum and complement. The suppressor cells occurred also in the thymus of unresponsive mice. Unresponsiveness was induced in mice immediately after priming with Lys and persisted at least up to 7 weeks after the induction. In contrast, suppressor cells appeared only 2 weeks after induction of unresponsiveness in both the spleen and the thymus but were no longer detectable 3-7 weeks later, although donor mice remained fully unresponsive. These results suggest that antigen-specific suppressor T cells are involved in the regulation of the expression of FPR only for a definite period of time in unresponsive mice.

In vitro lymphocyte stimulation in leprosy; simultaneous stimulation with Mycobacterium leprae antigens and phytohaemagglutinin

Peripheral blood lymphocytes from 105 subjects with different forms of leprosy and healthy contacts of leprosy patients were stimulated in vitro with different preparations of mycobacterial antigens alone or in combination with a suboptimal dose of phytohaemagglutinin (PHA). In nearly all individuals sonicated leprosy bacilli and PHA together gave a lower ³H-thymidine incorporation than did the same dose of PHA alone. There was no difference in the degree of inhibition seen in the different patient groups or the healthy contacts. High doses of whole, washed Mycobacterium leprae, combined with PHA led to an increased thymidine incorporation in borderline tuberculoid leprosy patients who had experienced a reversal reaction, and in healthy contacts with more than 6 months of exposure, while most lepromatous patients and contacts with less than 6 months exposure did not show an augmentation of the PHA-induced thymidine incorporation. The inhibition exerted by sonicated M. leprae was dose-dependent, seen even with very low doses of antigen, and was not due to direct cytotoxicity. M. bovis, strain BCG, was weakly suppressive in combination with PHA, and sonicated M. duvalii had a very marked suppressive effect. There was no correlation between the suppressive effect of M. leprae antigens and the other mycobacteria neither was there any correlation with the responses to the mycobacterial antigens alone. Many lepromatous leprosy patients showed significant suppression of background incorporation with addition of M. leprae antigens. This paper discusses whether the apparent `non-responsiveness' in lepromatous leprosy could be due to active suppressor mechanisms operative in vivo.