Dendritic cells and the regulation of a granulomatous immune response in the lung

To investigate the contribution of dendritic cells (DC) in a pulmonary granulomatous immune response, C57BL/l6 mice, nonimmunized or immunized with purified protein derivative (PPD) of Mycobacterium bovis, were intravenously injected with PPD-coated Sepharose-4B beads. One and three days later lungs were harvested, granuloma size was measured, and immunolabeled cells in granulomas were counted. On Day 1, granulomas in immunized mice were 3-fold larger and contained more major histocompatibility complex class II+, CD11c+ DCs than nonimmunized mice. By Day 3, these differences had diminished. In all granulomas MHC class II+, CD11c+ DCs were in contact with the beads. By in situ hybridization these DCs expressed interleukin (IL)-12 p40 mRNA. MOMA2+ macrophages were present throughout the granulomas, whereas CD4+ and CD8alpha+ T cells were localized at the granuloma periphery. DCs isolated from granulomatous lungs at Day 1, and from thoracic lymph nodes (LNs) at Days 1 and 3, stimulated PPD-specific T cell proliferation without exogenously added antigen, indicating that they had acquired bead-bound antigen. By Day 3, however, granuloma DCs presented little antigen, suggesting that newly immigrated DC lacked access to antigen or that antigen uptake/processing was inhibited. RNase protection assays of whole-lung mRNA showed increased interferon-gamma, IL-1beta, IL-1 receptor antagonist, IL-6, and macrophage inhibitory factor, but no IL-10 mRNA on Days 1 and 3. These observations support the premise that DCs are key in initiating granulomatous cell-mediated immunity. However, factors generated within the granuloma downregulate the antigen presenting function of DC by Day 3 in this experimental model.     

Mycobacterium bovis BCG-induced granuloma formation depends on gamma interferon and CD40 ligand but does not require CD28

Progressive granuloma formation is a hallmark of chronic mycobacterial infection. Granulomas are localized, protective inflammatory reactions initiated by CD4+ T cells, which contribute to control of bacterial growth and blockade of bacterial dissemination. In order to understand the costimulatory requirements that allow CD4+ T cells to directly or indirectly induce granulomas, we studied granuloma formation after 6 weeks in Mycobacterium bovis BCG-infected CD28- and CD40 ligand (CD40L)-deficient mice and compared it to granuloma formation in infected wild-type inbred mice and infected cytokine-deficient mice. We characterized granulomas morphologically in liver sections, analyzed granuloma infiltrating cells by flow cytometry, and measured cytokine production by cultured granuloma cells. CD28-deficient mice have no defect at the local inflammatory site, inasmuch as they form protective granulomas and control bacterial growth. However, there are fewer activated T cells in the spleen compared to infected wild-type animals, and quantitative differences in the cellular composition of the granuloma are observed by flow cytometry. In CD40L-deficient mice, the granuloma phenotype is very similar to the phenotype in gamma interferon (IFN-gamma)-deficient mice. Both IFN-gamma-deficient and CD40L-deficient mice form granulomas which prevent bacterial dissemination, but control of bacterial growth is significantly impaired. The relative proportion of CD4+ T cells in granulomas from both CD28(-/-) and CD40L(-/-) mice is significantly decreased compared with wild-type animals. Both models demonstrate that the phenotype and activation stage of systemic T cells do not always correlate with the phenotype and activation stage of the localized granulomatous response.     

Reciprocal action of interferon-gamma and interleukin-4 promotes granulomatous inflammation induced by Rhodococcus aurantiacus in mice.

An intravenous injection of Rhodococcus aurantiacus to mice causes granulomatous inflammation dependent on endogenous interferon-gamma (IFN-gamma). The present study examined the role of endogenous interleukin-4 (IL-4) on granulomatous inflammation. Endogenous IL-4 in the spleen extracts was not detected during the phase of granuloma formation by enzyme-linked immunosorbent assay (ELISA). However, IL-4 protein level was elevated during the phase of granuloma regression. IL-4 mRNA expression in the livers and spleens was also elevated during the phase of granuloma regression. In addition, IL-4 levels during the phase of granuloma formation were increased by treatment with anti-IFN-gamma monoclonal antibody (mAb), suggesting that endogenous IFN-gamma might inhibit IL-4 production during the phase of granuloma formation. Administration of anti-IL-4 mAb on weeks 3 and 4 after the inoculation inhibited the regression of granulomas and augumented IFN-gamma level at 5 weeks. Endogenous IFN-gamma was produced by CD4+ T cells during the phase of granuloma regression and endogenous IL-4 was produced by both CD4+ and CD8+ T cells. These findings suggest that during the phase of granuloma formation endogenous IL-4 might be inhibited by IFN-gamma, while during the phase of granuloma regression endogenous IL-4 might play a crucial role in the reduction of granulomas and IFN-gamma production.     

The Schistosoma japonicum egg granuloma.

Although Schistosoma japonicum egg granulomas are generally considered to be similar to those of S. mansoni (which are largely immunologic reactions of the delayed hypersensitivity type) there are suggestions that the histopathology and perhaps the etiology of the lesions are different. In mice with light S. japonicum infections, at 5 weeks after infection (2 weeks after egg production began), the livers contained 36,000 eggs each, but there was no reaction to the eggs, nor any evidence of hepatosplenic disease. By 6 weeks, large abscesses replete with cosinophils occurred around some of the eggs, and there was periportal inflammation consisting predominantly of plasma cells. From this time on, major lesions occurred mainly around large aggregates of eggs, and there was hepatosplenomegaly and portal hypertension. Living S. japonicum eggs injected into the pulmonary microvasculature of mice did not evoke significant granulomatous reactions on either primary or secondary exposure. Even when the eggs were injected into the lungs of infected animals, which had large granulomas around egg aggregates in the liver, little or no inflammatory reaction was seen around the eggs distributed singly throughout the pulmonary vessels. When the priming dose of eggs or soluble egg antigens was injected subcutaneously with or without complete Freund's adjuvant, significant granuloma formation occurred around eggs subsequently injected into the lungs. On the basis, therefore, of differences in the parasite factor (eggs) and host factors (histopathology and responses to routes of injection) it is suggested that the immunologic factors responsible for granuloma formation around S. mansoni and S. japonicum eggs may differ significantly.     

Unimpaired down-modulation of the hepatic granulomatous response in CD8 T-cell- and gamma interferon-deficient mice chronically infected with Schistosoma mansoni.

The granulomatous response to schistosome eggs is a CD4 T-cell-dependent, Th2-cytokine-dominated immunopathologic response. As infection proceeds to chronicity, both granuloma formation and egg-induced cytokine production become downregulated, and previous experiments have implicated CD8 T cells in this process. One mechanism by which CD8 T cells could suppress immunopathology is through the production of the counterregulatory cytokine gamma interferon (IFN-gamma), but no in vivo evidence exists to directly support this hypothesis. In this study, we analyzed hepatic granuloma formation and egg-induced cytokine production in Schistosoma mansoni-infected gene knockout mice deficient in either CD8 lymphocytes or IFN-gamma. Surprisingly, we found that neither immunologic component plays an essential function in the control of granuloma and cytokine responses during either the acute or chronic stage of infection. Thus, other mechanisms may be more important in the regulation of immunopathology in schistosomiasis.     

Identification of larval cross-reactive and egg-specific antigens involved in granuloma formation in murine schistosomiasis mansoni.

Cross-reactive humoral immune responses between antigens of different developmental stages of the worm Schistosoma mansoni have previously been demonstrated. In contrast, information on antigenic cross-reactivity at the T-cell level is still very sparse. The present study examined the cross-reactive T-cell responses to eggs and crude and fractionated soluble egg antigens (SEA) in infected mice prior to (from 0 to 4 weeks of infection) and after (5 weeks and onwards) egg deposition. Splenic lymphocyte proliferation to unfractionated SEA was detected as early as 2 weeks postinfection and increased rapidly by 4 weeks postinfection. Injections of live eggs into the lungs of infected mice at 4 weeks postinfection demonstrated enhanced granuloma formation, indicating the presence of primed T cells that respond to egg antigens. Further experiments with the artificial granuloma model and polyacrylamide gel electrophoresis-separated SEA fractions demonstrated that in mice infected for 4 weeks the 60- to 66-, 93- to 125-, and greater than 200-kDa SEA fraction-coated beads elicited significant pulmonary granulomas. By 6 weeks postinfection, when eggs are deposited in the livers, in addition to the cross-reactive fractions (60 to 66, 93 to 125, and greater than 200 kDa), beads coated with fractions of 25 to 30, 32 to 38, and 70 to 90 kDa also elicited significant granulomatous reactions. These antigenic fractions are considered to have elicited egg stage-specific T-cell responsiveness. In addition hepatic granuloma T cells from the 6th week of infection demonstrated the strongest blastogenic response to the 60- to 66-kDa cross-reactive fraction. Thus, in vitro and in vivo experiments demonstrated T-cell cross-reactivity between the larval and egg stages of the worm. On the basis of these observations, the appearance of the primary circumovum granulomatous response in infected mice is considered to represent the sum of larval cross-reactive and egg-specific T-cell responsiveness.     

Anti-L3T4 antibody treatment suppresses hepatic granuloma formation and abrogates antigen-induced interleukin-2 production in Schistosoma mansoni infection

In murine schistosomiasis mansoni, granulomatous inflammation is an immune response that involves egg antigen presentation to T cells in the context of class II major histocompatibility complex determinants and subsequent inflammatory lymphokine production by delayed-hypersensitivity (TDH) lymphocytes. In the present study, monoclonal antibodies directed against L3T4, I-A, and Lyt-2 molecules were injected intraperitoneally into S. mansoni-infected mice to study the role of these membrane antigens in the process of granuloma formation. A dramatic suppression of the hepatic granuloma size and antigen-induced interleukin-2 (IL-2) production by spleen cells was seen in mice that received anti-L3T4 monoclonal antibody treatment. The total number of cells, especially the L3T4+ T cells, was greatly diminished in the spleens. Furthermore, histopathological study of the granulomas in stained liver sections demonstrated the paucity of eosinophils and macrophages, absence of epithelioid cells and multinucleated giant cells, and minimal collagen deposition within the lesions. Damaged hepatocytes were also seen surrounding these ill-formed granulomas. In contrast, anti-I-A monoclonal antibody treatment partially suppressed IL-2 production, although granuloma size and cellular composition remained the same. Mice that received anti-Lyt-2 monoclonal antibody did not show any changes in either IL-2 production or hepatic granulomatous inflammation. The data presented in this paper indicate a crucial role for L3T4 molecules present on a subset of class II major histocompatibility complex-restricted TDH cells in IL-2 production and the generation of the granulomatous response.     

Granuloma cells in chronic inflammation express CD205 (DEC205) antigen and harbor proliferating T lymphocytes: Similarity to antigen‐presenting cells

Granulomas are classified as immune or foreign body granulomas. Of these, the immune granulomas, a hallmark of granulomatous inflammation, are closely related to cell‐mediated immune responses. The aim of the present study is to characterize immune granuloma cells in 33 patients with granulomatous inflammation focusing on the expression of CD205 (DEC205), a cell surface marker of antigen presenting cells, and their spatial relationship to T cells. CD205 was frequently expressed by immune granuloma cells, in contrast to foreign body granuloma cells that lacked CD205 expression. T cells were not only distributed in a lymphocyte collar around the granuloma, but also present among the granuloma cells (termed ‘intra‐granuloma T cells’). Intra‐granuloma T cells stained positive for Ki‐67 (median positivity = 9.4%) by double immunostaining for CD3 and Ki‐67. This indicated the presence of proliferative stimuli within the granuloma that could activate the intra‐granuloma T cells. The labeling index of Ki‐67 in intra‐granuloma T cells was significantly higher than that of T cells in the lymphocyte collar (P < 0.0001) or T cells in the T cell zone (paracortex) of chronic tonsillitis or reactive lymphadenitis (P = 0.002). These data indicate a close similarity between immune granulomas and antigen presenting cells.     

Temporal and spatial arrangement of lymphocytes within lung granulomas induced by aerosol infection with Mycobacterium tuberculosis

The progression of the immune response in the lungs after aerosol infection with Mycobacterium tuberculosis is a complex cellular event dominated by macrophages and lymphocytes. Although the phenotype of lymphocytes participating in this response is becoming increasingly well characterized, the dynamic influx of these cells during the infection and their spatial arrangements within the lung tissue are still poorly understood. This study shows that in the first month after aerosol infection with M. tuberculosis there was a steady increase in the percentages of total CD3+, CD3+ CD4+ and CD3+ CD8+ cells, with consistently larger numbers of CD3+ CD4+ cells than of CD3+ CD8+ cells. As granuloma formation continued, the granuloma was found to consist of macrophages, CD4, and CD8 T cells, as well as a smaller number of B cells. Whereas CD4 T cells formed organized aggregates, CD8 T cells were fewer and more scattered and tended to be more prominent toward the periphery of the granulomas. The possible ramifications of the juxtapositions of these two major T-cell subsets are discussed.     

Splenic and granuloma T-lymphocyte responses to fractionated soluble egg antigens of Schistosoma mansoni-infected mice.

Soluble egg antigens (SEA) secreted by the eggs of Schistosoma mansoni worms induce a T-cell-mediated granulomatous response that is principally responsible for the pathology of the disease. In the present study sodium dodecyl sulfate-polyacrylamide gel electrophoresis-separated SEA proteins were divided into nine fractions (less than 21, 25 to 30, 32 to 38, 40 to 46, 50 to 56, 60 to 66, 70 to 90, 93 to 125, and greater than 200 kDa), electroeluted, and utilized in in vitro lymphoproliferation assays. T-cell-enriched spleen cells from acutely infected mice responded to all nine fractions, while those from chronically infected mice responded to only the 50- to 56- and the 60- to 66-kDa fractions. Depletion of the CD4+ T-cell subset among acute and chronic-infection spleen cells abrogated the response. Depletion of the CD8+ T-cell population resulted in increased proliferation in response to fractions by acute-infection T cells and facilitated responsiveness to hitherto-inactive SEA fractions in chronic-infection T cells. Acute-infection CD4+ granuloma T cells responded to the 40- to 46-, 50- to 56-, 70- to 90-, 93- to 125-, and greater than 200-kDa fractions, while the chronic-infection granuloma T cells responded only to the greater than 200-kDa fraction of SEA. Selective depletion of the CD4+ T-cell subset when acute-infection granuloma lymphocytes were tested abrogated proliferation, whereas subset depletions when chronic-infection granuloma cells were tested indicated that both CD4+ and CD8+ T cells respond to the greater than 200-kDa fraction. The present study reveals differences between acute- and chronic-infection splenic and granuloma T cells in the pattern of T-cell blastogenic responses to fractionated SEA.     

Immunohistochemical detection of interferon-gamma-producing cells in granuloma formation of sporotrichosis.

Granuloma formation is a common response in the skin infection of sporotrichosis. The involvement of interferon-gamma (IFN-gamma) and inducible nitric oxide synthase (iNOS) in the granuloma formation of sporotrichosis is less known. The aim of this study was to describe by immunohistochemistry the exact tissue distribution of IFN-gamma-positive cells and iNOS-positive cells in the granuloma of skin lesions from patients with sporotrichosis. Formalin-fixed paraffin-embedded skin biopsy sections from five patients were stained by immunohistochemical methods. Mixture of CD4-positive T cells and CD8-positive T cells were present in and around the granulomatous lesions. IFN-gamma-positive cells, like mononuclear lymphoid cells, were detected in the periphery of the granulomas in all samples. The pattern of IFN-gamma staining appeared to be a combination of intracellular staining in mononuclear lymphoid cells and extracellular deposition in the surrounding tissue. The majority of the epitheloid cells and multinucleated giant cells within the granuloma were identified by immunostaining for CD68. In contrast, no expression of immunoreactive iNOS was observed in those cells in all samples. These findings indicate that granulomas of sporotrichosis are coupled with Th1 response.     

T cells expressing the γδ T cell receptor are not required for egg granuloma formation in schistosomiasis

Immunopathology in schistosomiasis consists of a granulomatous response around parasite eggs. It has been established that granuloma formation is mediated by CD4⁺ T helper cells. However, the role of T cells bearing the γδ T cell receptor (TCR) has not been determined. In this study we utilized mutant mice that lack either αβ or γδ T cells as a result of gene targeting to investigate the relative roles of αβ and γδ T cells in the induction of immunopathology related to schistosomiasis. Mutant and control mice were infected with Schistosoma mansoni and granuloma formation as well as lymph node cell proliferative responses to egg antigens were analyzed after 8 weeks. TCR δ mutant mice (lacking γδ T cells) displayed vigorous formation of egg granulomas that were not significantly different from those observed in normal controls, both in terms of granuloma size and cellular composition. In contrast, TCR α and TCR β mutant mice (lacking αβ T cells) were unable to form granulomas. Moreover, mesenteric lymph node cells from TCR δ mutant and control mice responded strongly to egg antigens in vitro, while TCR α and β mutant mice did not. Our studies show that in schistosomiasis granuloma formation and proliferative responses to egg antigens are strictly dependent on αβ T cells. They also suggest that γδ T cells by themselves can neither mediate a granulomatous inflammation, nor significantly modify one mediated by αβ T cells.     

Chemokine production during hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) is an interstitial lung disease that develops following repeated exposure to inhaled particulate antigens. Individuals with HP develop lymphocytic alveolitis,granuloma formation, and fibrosis. HP is categorized as a Th1 disease, and granuloma formation is dependent on T cells and the Th1 cytokine IFN-gamma. We therefore hypothesized that the IFN-gamma-inducible chemokines IP-10, Mig, and I-TAC, which are frequently associated with Th1 diseases, would play an important role in the pathogenesis of disease. We analyzed the expression of multiple chemokines in the lungs of wild-type (WT) and IFN-gamma-knockout (GKO) mice exposed to the particulate antigen Saccharopolyspora rectivirgula (SR). Our results demonstrate the production of IP-10, Mig, and I-TAC in WT mice during the development of HP, whereas GKO mice have reduced levels of IP-10 and no Mig or I-TAC mRNA in the lungs in response to SR exposure. The production of these chemokines is associated with an influx of CXCR3+/CD4+ T cells into lungs of WT mice, which is reduced in GKO mice. These results suggest that IFN-gamma mediates the recruitment of CXCR3+/CD4+ T cells into the lung via production of the chemokines IP-10, Mig, and I-TAC, resulting in granuloma formation.     

Culture of Regulatory T-Cell Lines from Bronchial Mucosa

T lymphocytes play a major role in many immune responses. In the last decade, special focus has been on the function of Th1 and Th2 effector cells. Now the importance of regulatory CD4⁺CD25⁺ T cells in maintenance of the immunological homeostasis emerges. Sarcoidosis is a multisystem granulomatous disorder often affecting the lungs. The typical sarcoid granulomas consists of epitheloid cells, macrophages and lymphocytes, mainly CD4⁺ T cells of Th1 phenotype. We have cultured T cells from bronchial biopsies of patients with sarcoidosis as well as from controls in high levels of interleukin 2 (IL-2) and IL-4 and demonstrate spontaneously arising CD4⁺ CD25⁺ populations and high concentrations of IL-10 in these cultures. The main difference between cultures of sarcoid origin compared to controls is a very much higher concentration of the inflammatory cytokines IL-6 and TNF-α in cultures of sarcoid origin.     

当归对体内外血吸虫卵肉芽肿反应抑制作用的实验研究

目的:验证中药当归制剂对虫卵诱发的肉芽肿反应有无直接抑制作用。方法:将曰本血吸虫活卵悬液经尾静脉给致敏的ICR小鼠定量注入, 在小鼠肺部建立体内肉芽肿反应模型, 再经腹腔给用药组小鼠注射当归制剂;另取肺模型鼠及曰本血吸虫急性感染鼠脾细胞进行体外培养, 在培养系统中加入曰本血吸虫干卵, 从而建立围绕虫卵的体外肉芽肿反应模型, 根据围绕虫卵反应的细胞数确定反应强度(反应指数, RI).测定肺单卵肉芽肿直径及观察培养液中加入当归制剂对反应强度的影响等。结果:体内用药后, 给药组小鼠肺肉芽肿平均直径显著小于对照组(P<005), 肉芽肿反应增长比显著低于对照组(P<0.01);给药组小鼠脾细胞在体外围绕虫卵的反应在加卵后第5d起明显弱于对照组(P<0.01或P<005);在培养液中加入当归制剂后可使感染鼠脾细胞的RI显著下降(P<0.01或P<005), 并有一定的剂量效应。结论:中药当归制剂在体内外模型中给药均可明显抑制由虫卵诱发的肉芽肿性炎症反应。     

Transfer of a CD4+ Th1 cell line to nude mice effects clearance of Rhodococcus equi from the lung.

Rhodococcus equi, and intracellular respiratory pathogen, causes sever e granulomatous pneumonia in humans with AIDS and in young horses. Pulmonary clearance of R. equi requires functional CD4+ T cells and gamma interferon (IFN-gamma) expression from bronchial lymph node cells. The purpose of this study was to investigate whether R. equi-specific CD4+ Th1 cells could effect clearance of R. equi from the lung. Adoptive transfer of a clearance of R. equi from the lungs. In contrast, mice transfused with a R. equi-specific CD4+ Th2 cell line expressed interleukin-4 but not IFN-gamma mRNA, failed to clear pulmonary infection, and developed granulomas in the lung. Control mice, which did not receive cells, did not produce IFN-gamma or interleukin-4 and developed small pulmonary granulomas. These results clearly show that a Th1 response is sufficient to effect pulmonary clearance of R. equi.     

Establishment and characterization of an antigen-specific T-cell line from liver granulomas of Schistosoma mansoni-infected mice.

Granulomatous inflammations in schistosomiasis mansoni are the result of T-cell-mediated reactions to soluble egg antigens (SEA) secreted by parasite ova. To study TDH effector cell function, a granuloma T-cell line was established from collagenase-digested liver granulomas of acutely infected CBA/J mice. Dispersed nonadherent granuloma cells were cultured with feeder layer cells and SEA or with feeder layer cells alone in alternate cycles for 32 weeks. The granuloma T-cell line was L3T4+ Lyt-1+. In vitro, the SEA-stimulated T cells showed proliferation and interleukin 2 production. One million T cells adoptively transferred SEA-specific footpad swelling, and 7.5 X 10(6) T cells adoptively transferred granulomatous hypersensitivity to injected ova or SEA-coated beads. Anti-L3T4 monoclonal antibody blocked the SEA-specific cell proliferation. Depletion of L3T4+ cells abrogated, while that of Lyt-1+ cells diminished the adoptive transfer of SEA-specific footpad swelling. These experiments demonstrate that the granuloma T-lymphocyte population contains TDH-type effector cells. Establishment of an SEA-specific granuloma T-cell line will allow the study of the effector functions of the hitherto uncharacterized intralesional granuloma T lymphocyte.     

Exogenously administered prostaglandins modulate pulmonary granulomas induced by Schistosoma mansoni eggs

The inflammatory modulating activity of specific prostaglandins has been examined for both immune and foreign-body types of pulmonary granulomas. Lung granuloma formation generated in mice by embolization of Schistosoma mansoni eggs was markedly suppressed by treatment with the stable, functional analog of prostaglandin E, (PGE1), (15-(S)-15-methyl PGE1) while treatment with PGF2 alpha augmented the granulomatous response. Despite marked effects on egg-induced granuloma formation, PGs had no significant effect on the foreign body lesion induced by Sephadex beads. Likewise, PGs had no effect on the primary antibody response to schistosome egg antigens. However, notable derangements in splenic lymphoid populations occurred. While T-cell numbers appeared constant in face of PG treatment, B-cell populations were depressed by methyl-PGE1 and augmented by PGF2 alpha. Further analysis revealed that methyl-PGE1 appeared to suppress both the induction and elicitation phases of the cell-mediated response to schistosome eggs. Cyclophosphamide treatment could partially reverse this suppression, but the induction of suppressor cell activity was not solely responsible for this effect. The possible role and mechanism of PGs as modulators of chronic inflammation is discussed.     

Experimental production of pulmonary granulomas; II. Age dependency and immune modulation of granuloma production.

Endobronchial instillation of Freund''s complete adjuvant (FCA) induced epithelioid cell granulomas in the lungs of juvenile rabbits which had been kept free from contamination with the microbiol antigens. The granulomas were named "juvenile granulomas", because, unlike FCA granulomas in adult animals, prior immunization was unnecessary for their induction. The granulomas developed in several weeks with a peak at 14 weeks of age, after which the production decreased gradually. The rate of granuloma production seemed to vary with the acquisition of skin hypersensitivity to tuberculin (OT), suggesting that granuloma production, as well as skin hypersensitivity, is in the category of T-dependent immune reactions. In fact, T-generating lymphoid organs developed in parallel with the dermal and pulmonary reactions. Thus, juvenile rabbits at about 14 weeks of age are most susceptible to the microbial antigens. This susceptibility results in the unexpected production of immune granulomas in response to depot antigens at the site of instillation. The treatment of foetal or neonatal rabbits with FCA markedly suppressed granuloma production in juveniles but not in adults and did suppress but gradually enhanced the tuberculin skin reaction. It is suggested that generation of suppressor T cells is the cause of suppression of juvenile granuloma production.