Nuclear medicine imaging in tuberculosis using commercially available radiopharmaceuticals

Green synthesis, radioiodination and in vivo biodistribution of 5-(2-hydroxyphenyl)-2,4-dihydro-3H-pyrazol-3-one derivatives as potential candidates for lung imaging

Lung targeting was developed by synthesising pyrazolone derivatives 6a-f under solvent-free and thermal conditions by reacting azo coumarins 4a-c with hydrazines 5a and b using maltose as a biodegradable catalyst. Different spectral data characterized the synthesized agents as proton-NMR, FT-IR, and mass spectra. Direct radioiodination with iodine-131 was performed and optimized to reach the highest radiochemical purities (92 ± 0.47 to 98 ± 0.21%) using chloramine-T, a moderate oxidizing agent. The 131I-pyrazolone derivatives were confirmed based on HRMS. Furthermore, radioiodinated nitro-derivatives accumulated well in the lung of normal mice during in vivo evaluation, and the better uptake was for nitrophenyl-derivative 7f, about 30.06 ± 0.04% at 30 min after injection. Consequently, synthesized radioiodinated derivatives may be employed as prospective tracers for lung perfusion scans.

From Pixels to Pathology: Employing Computer Vision to Decode Chest Diseases in Medical Images

Radiology has been a pioneer in the healthcare industry's digital transformation, incorporating digital imaging systems like picture archiving and communication system (PACS) and teleradiology over the past thirty years. This shift has reshaped radiology services, positioning the field at a crucial junction for potential evolution into an integrated diagnostic service through artificial intelligence and machine learning. These technologies offer advanced tools for radiology's transformation. The radiology community has advanced computer-aided diagnosis (CAD) tools using machine learning techniques, notably deep learning convolutional neural networks (CNNs), for medical image pattern recognition. However, the integration of CAD tools into clinical practice has been hindered by challenges in workflow integration, unclear business models, and limited clinical benefits, despite development dating back to the 1990s. This comprehensive review focuses on detecting chest-related diseases through techniques like chest X-rays (CXRs), magnetic resonance imaging (MRI), nuclear medicine, and computed tomography (CT) scans. It examines the utilization of computer-aided programs by researchers for disease detection, addressing key areas: the role of computer-aided programs in disease detection advancement, recent developments in MRI, CXR, radioactive tracers, and CT scans for chest disease identification, research gaps for more effective development, and the incorporation of machine learning programs into diagnostic tools.

Recent applications of CBT-Cys click reaction in biological systems

Click chemistry is a hot topic in many research fields. A biocompatible reaction from fireflies has attracted increasing attention since 2009. Herein, we focus on the firefly-sourced click reaction between cysteine (Cys) and 2-cyanobenzothiazole (2-CBT). This reaction has many excellent properties, such as rapidity, simplicity and high selectivity, which make it successfully applied in protein labeling, molecular imaging, drug discovery and other fields. Meanwhile, its unique ability to form nanoparticles expands its applications in biological systems. We review its principle, development, and latest applications in the past 5 years and hope this review provides more profound and comprehensive insights to its further application.

Tuberculosis: Role of Nuclear Medicine and Molecular Imaging With Potential Impact of Neutrophil-Specific Tracers

With Tuberculosis (TB) affecting millions of people worldwide, novel imaging modalities and tools, particularly nuclear medicine and molecular imaging, have grown with greater interest to assess the biology of the tuberculous granuloma and evolution thereof. Much early work has been performed at the pre-clinical level using gamma single photon emission computed tomography (SPECT) agents exploiting certain characteristics of Mycobacterium tuberculosis (MTb). Both antituberculous SPECT and positron emission tomography (PET) agents have been utilised to characterise MTb. Other PET tracers have been utilised to help to characterise the biology of MTb (including Gallium-68-labelled radiopharmaceuticals). Of all the tracers, 2-[¹⁸F]FDG has been studied extensively over the last two decades in many aspects of the treatment paradigm of TB: at diagnosis, staging, response assessment, restaging, and in potentially predicting the outcome of patients with latent TB infection. Its lower specificity in being able to distinguish different inflammatory cell types in the granuloma has garnered interest in reviewing more specific agents that can portend prognostic implications in the management of MTb. With the neutrophil being a cell type that portends this poorer prognosis, imaging this cell type may be able to answer more accurately questions relating to the tuberculous granuloma transmissivity and may help in characterising patients who may be at risk of developing active TB. The formyl peptide receptor 1(FPR1) expressed by neutrophils is a key marker in this process and is a potential target to characterise these areas. The pre-clinical work regarding the role of radiolabelled N-cinnamoyl –F-(D) L – F – (D) –L F (cFLFLF) (which is an antagonist for FPR1) using Technetium 99m-labelled conjugates and more recently radiolabelled with Gallium-68 and Copper 64 is discussed. It is the hope that further work with this tracer may accelerate its potential to be utilised in responding to many of the current diagnostic dilemmas and challenges in TB management, thereby making the tracer a translatable option in routine clinical care.

A novel dipeptide coupled with pyrazine-oxadiazole derivative as a potential antitubercular agent: Synthesis, radioiodination and bioevaluation

Tuberculosis (TB) is a disease caused by Mycobacterium and usually attack the lung. Synthesis of new dipeptide derivatives attached to antitubercular active heterocyclic rings like pyrazine and 1,3,4-oxadiazole called ethyl 2-(2-(5-((pyrazin-2-ylamino) methyl)-1,3,4-oxadiazol-2-ylthio) acetamido) acetamido)-3-(4-hydroxyphenyl) propanoate (EPOGTP) and iodinated EPOGTP are reported. The compounds have been characterized by mass, FT-IR and ¹H NMR spectroscopy. Their in vitro investigation against Mycobacterium tuberculosis cell line indicated good IC₅₀value of 210 μg/ml for EPOGTP and 86 μg/ml for iodo-EPOGTP. For study the biodisriution, the direct radioiodination of EPOGTP with iodine-131 using mild oxidizing agent, N-Bromosuccinimide (NBS), was performed and optimized for obtaining the maximum radiochemical purity (97.3 ± 0.47%). Then, the in vivo biodistribution in healthy mice showed good accumulation of radioiodinated EPOGTP in lung of about 41.83 ± 0.23% (the percentage of injected dose per gram of organ) at 15 min post-injection. As a conclusion, the synthetized dipeptide and its iodinated derivative could be further evaluated as a potential antitubercular agents.

Current Applications for Nuclear Medicine Imaging in Pulmonary Disease

Purpose of Review

The main goal of the article is to familiarize the reader with commonly and uncommonly used nuclear medicine procedures that can significantly contribute to improved patient care. The article presents examples of specific modality utilization in the chest including assessment of lung ventilation and perfusion, imaging options for broad range of infectious and inflammatory processes, and selected aspects of oncologic imaging. In addition, rapidly developing new techniques utilizing molecular imaging are discussed.

Recent Findings

The article describes nuclear medicine imaging modalities including gamma camera, SPECT, PET, and hybrid imaging (SPECT/CT, PET/CT, and PET/MR) in the context of established and emerging clinical applications. Areas of potential future development in nuclear medicine are discussed with emphasis on molecular imaging and implementation of new targeted tracers used in diagnostics and therapeutics (theranostics).

Summary

Nuclear medicine and molecular imaging provide many unique and novel options for the diagnosis and treatment of pulmonary diseases. This article reviews current applications for nuclear medicine and molecular imaging and selected future applications for radiopharmaceuticals and targeted molecular imaging techniques.

SPECT/CT Imaging of Mycobacterium tuberculosis Infection with [125I]anti-C3d mAb

PURPOSE

Diagnosis and therapeutic monitoring of chronic bacterial infection requires methods to detect and localize sites of infection accurately. Complement C3 activation fragments are generated and covalently bound to selective bacterial pathogens during the immune response and can serve as biomarkers of ongoing bacterial infection. We have developed several probes for detecting tissue-bound C3 deposits, including a monoclonal antibody (mAb 3d29) that recognizes the tissue-bound terminal processing fragments iC3b and C3d but does not recognize native circulating C3 or tissue-bound C3b.

PROCEDURES

To determine whether mAb 3d29 could be used to detect chronic Mycobacterium tuberculosis infection non-invasively, aerosol-infected female C3HeB/FeJ mice were injected with [¹²⁵I]3d29 mAb and either imaged using single-photon emission computed tomography (SPECT)/X-ray computed tomography (CT) imaging at 24 and 48 h after radiotracer injection or being subjected to biodistribution analysis.

RESULTS

Discrete lesions were detected by SPECT/CT imaging in the lungs and spleens of infected mice, consistent with the location of granulomas in the infected animals as detected by CT. Low-level signal was seen in the spleens of uninfected mice and no signal was seen in the lungs of healthy mice. Immunofluorescence microscopy revealed that 3d29 in the lungs of infected mice co-localized with aggregates of macrophages (detected with anti-CD68 antibodies). 3d29 was detected in the cytoplasm of macrophages, consistent with the location of internalized M. tuberculosis. 3d29 was also present within alveolar epithelial cells, indicating that it detected M. tuberculosis phagocytosed by other CD68-positive cells. Healthy controls showed very little retention of fluorescent or radiolabeled antibody across tissues. Radiolabeled 3d29 compared with radiolabeled isotype control showed a 3.5:1 ratio of increased uptake in infected lungs, indicating specific uptake by 3d29.

CONCLUSION

3d29 can be used to detect and localize areas of infection with M. tuberculosis non-invasively by 24 h after radiotracer injection and with high contrast.

Novel Quantitative PET Imaging Techniques in Tuberculosis

The role of fluorodeoxyglucose (FDG)-PET/computed tomography (CT) in tuberculosis (TB) continues to expand in disease detection, assessment of the extent of the disease, and treatment response monitoring. This article reviews available data regarding the use of FDG-PET/CT in patients with TB. A new method of quantification for patients with TB is introduced. This method produces robust parameters that represent the total disease burden.

[18F-FDG PET/CT manifestations of massive type active pulmonary tuberculosis and its differentiation from lung cancer]

OBJECTIVE

To investigate 18F-FDG PET/CT manifestations of massive type active tuberculosis and lung cancer and the differential diagnosis of the two diseases based on 18F-FDG PET/CT findings.

METHODS

We retrospectively collected the data from 74 patients with active tuberculosis and 64 patients with lung cancer, whose lesions presented as solid masses on CT. The demographic and clinical data of the patients, 18F-FDG PET characteristics including SUVmax, 18F-FDG uptake (higher than mediastinal blood pool or not), radioactive defect within the lesion, and the CT findings including the lesion size, signs of cavity, vacuoles, lobulation, smooth border, and mediastinal/lung window ratio (M/L ratio) of the lesions were analyzed. Univariate and multivariate analyses were used to compare the variables between the two groups, and a logistic regression model was established for differentiation of the two diseases. The diagnostic efficiency was evaluated by area under the receiver-operating characteristic (ROC) curve analysis.

RESULTS

No significant differences were found in the quantitative index (SUVmax >2.5 or not) or in the qualitative index (uptake of lesion higher than mediastinal blood pool or not) in PET between massive type active tuberculosis and lung cancer (P>0.05). Univariate analysis revealed that SUVmax, 18F-FDG uptake of the lesion, age, lesion size, signs of cavity, or M/L ratio were not significantly different (P>0.05), but gender, signs of radioactive defect, vacuoles, smooth border and lobulation were significantly different (P < 0.05) between the two diseases. Multivariate analysis showed that gender, signs of radioactive defect, smooth border and lobulation of the lesion were independent factors for discrimination of the two diseases (P < 0.05). A risk prediction model for active tuberculosis was established based on logistic regression analysis: P=1/(1+e-x), X=-0.530+1.978×gender+3.343×radioactive defect +2.846×smooth border-2.116×lobulation. For diagnosis of active tuberculosis, the sensitivity, specificity, accuracy, positive predictive value and negative predictive value of this model were 78.4%, 92.2%, 84.8%, 92.1%, and 78.7%, respectively.

CONCLUSIONS

The combined analysis of gender, signs of radioactive defect, smooth border and lobulation of the lesions is useful for discriminating massive type active tuberculosis from lung cancer in the majority of the patients, whereas 18F-FDG uptake alone has only limited value for a differential diagnosis.

Tuberculosis

Tuberculosis (TB) is currently the world's leading cause of infectious mortality. Imaging plays an important role in the management of this disease. The complex immune response of the human body to Mycobacterium tuberculosis results in a wide array of clinical manifestations, making clinical and radiological diagnosis challenging. ¹⁸F-FDG-PET/CT is very sensitive in the early detection of TB in most parts of the body; however, the lack of specificity is a major limitation. ¹⁸F-FDG-PET/CT images the whole body and provides a pre-therapeutic metabolic map of the infection, enabling clinicians to accurately assess the burden of disease. It enables the most appropriate site of biopsy to be selected, stages the infection, and detects disease in previously unknown sites. ¹⁸F-FDG-PET/CT has recently been shown to be able to identify a subset of patients with latent TB infection who have subclinical disease. Lung inflammation as detected by ¹⁸F-FDG-PET/CT has shown promising signs that it may be a useful predictor of progression from latent to active infection. A number of studies have identified imaging features that might improve the specificity of ¹⁸F-FDG-PET/CT at some sites of extrapulmonary TB. Other PET tracers have also been investigated for their use in TB, with some promising results. The potential role and future perspectives of PET/CT in imaging TB is considered. Literature abounds on the very important role of ¹⁸F-FDG-PET/CT in assessing therapy response in TB. The use of ¹⁸F-FDG for monitoring response to treatment is addressed in a separate review.

Monitoring Response to Therapy

Monitoring response to treatment is a key element in the management of infectious diseases, yet controversies still persist on reliable biomarkers for noninvasive response evaluation. Considering the limitations of invasiveness of most diagnostic procedures and the issue of expression heterogeneity of pathology, molecular imaging is better able to assay in vivo biologic processes noninvasively and quantitatively. The usefulness of ¹⁸F-FDG-PET/CT in assessing treatment response in infectious diseases is more promising than for conventional imaging. However, there are currently no clinical criteria or recommended imaging modalities to objectively evaluate the effectiveness of antimicrobial treatment. Therapeutic effectiveness is currently gauged by the patient's subjective clinical response. In this review, we present the current studies for monitoring treatment response, with a focus on Mycobacterium tuberculosis, as it remains a major worldwide cause of morbidity and mortality. The role of molecular imaging in monitoring other infections including spondylodiscitis, infected prosthetic vascular grafts, invasive fungal infections, and a parasitic disease is highlighted. The role of functional imaging in monitoring lipodystrophy associated with highly active antiretroviral therapy for human immunodeficiency virus is considered. We also discuss the key challenges and emerging data in optimizing noninvasive response evaluation.

68Ga-NOTA-Functionalized Ubiquicidin: Cytotoxicity, Biodistribution, Radiation Dosimetry, and First-in-Human PET/CT Imaging of Infections

Ubiquicidin is an antimicrobial peptide with great potential for nuclear imaging of infectious diseases, as its cationic-rich fragment TGRAKRRMQYNRR (UBI) has been functionalized with NOTA to allow complexation to ⁶⁸Ga (⁶⁸Ga-NOTA-UBI). We herein assess the cytotoxicity and radiation dosimetry for ⁶⁸Ga-NOTA-UBI and a first-in-human evaluation to diagnose infectious processes. Methods: Cytotoxicity was evaluated in green monkey kidney epithelial (Vero) cells and MT-4 leukocytes. Tracer susceptibility was studied in vitro using different bacterial and fungal strains. PET/CT-based biodistribution, pharmacokinetics, and radiation dosimetry were performed on nonhuman primates. Two healthy volunteers and 3 patients with suspected infection underwent ⁶⁸Ga-NOTA-UBI PET/CT imaging. Results: Negligible cytotoxicity was determined for NOTA-UBI. ⁶⁸Ga-NOTA-UBI showed moderate blood clearance (29-min half-life) and predominant renal clearance in nonhuman primates. Human radiation dose estimates indicated the bladder wall as the dose-critical tissue (185 μSv/MBq), followed by the kidneys (23 μSv/MBq). The total absorbed body dose was low (<7 μSv/MBq); the effective dose was estimated at 17 μSv/MBq. ⁶⁸Ga-NOTA-UBI could diagnose bone- and soft-tissue infection in 3 of 3 patients. Conclusion:⁶⁸Ga-NOTA-UBI is considered a nontoxic, safe-to-administer radiopharmaceutical unlikely to cause adverse effects in humans. The favorable tracer biodistribution and the first-in-human results will make ⁶⁸Ga-NOTA-UBI PET/CT an encouraging future diagnostic technique with auxiliary clinical relevance.

Modeling the respiratory motion of solitary pulmonary nodules and determining the impact of respiratory motion on their detection in SPECT imaging

The objectives of this investigation were to model the respiratory motion of solitary pulmonary nodules (SPN) and then use this model to determine the impact of respiratory motion on the localization and detection of small SPN in SPECT imaging for four reconstruction strategies. The respiratory motion of SPN was based on that of normal anatomic structures in the lungs determined from breath-held CT images of a volunteer acquired at two different stages of respiration. End-expiration (EE) and time-averaged (Frame Av) non-uniform-B-spline cardiac torso (NCAT) digital-anthropomorphic phantoms were created using this information for respiratory motion within the lungs. SPN were represented as 1 cm diameter spheres which underwent linear motion during respiration between the EE and end-inspiration (EI) time points. The SIMIND Monte Carlo program was used to produce SPECT projection data simulating Tc-99m depreotide (NeoTect) imaging. The projections were reconstructed using 1) no correction (NC), 2) attenuation correction (AC), 3) resolution compensation (RC), and 4) attenuation correction, scatter correction, and resolution compensation (AC_SC_RC). A human-observer localization receiver operating characteristics (LROC) study was then performed to determine the difference in localization and detection accuracy with and without the presence of respiratory motion. The LROC comparison determined that respiratory motion degrades tumor detection for all four reconstruction strategies, thus correction for SPN motion would be expected to improve detection accuracy. The inclusion of RC in reconstruction improved detection accuracy for both EE and Frame Av over NC and AC. Also the magnitude of the impact of motion was least for AC_SC_RC.

Malignant disease as an incidental finding at ¹⁸F-FDG-PET/CT scanning in patients with granulomatous lung disease

PURPOSE

Fluorine-18 fluorodeoxyglucose (¹⁸F-FDG)-PET/computed tomography (CT) is used for assessment of the extent and activity of disease in patients with inflammatory granulomatous lung disease, in particular sarcoidosis and tuberculosis. The aim of this retrospective analysis was to assess the value of ¹⁸F-FDG-PET/CT in the identification of previously unknown malignant disease during routine investigation of granulomatous lung disease.

MATERIALS AND METHODS

From July 2008 to December 2013, a total of 122 patients with tuberculosis (76 male and 46 female patients; age range 19.6-88.6 years, mean 52.8±16.6 years) and 85 patients with sarcoidosis (46 male and 39 female patients; age range 17.8-76.5 years, mean 48.6±13.8 years) underwent ¹⁸F-FDG-PET/CT. Reports were generated in consensus by both a nuclear medicine physician and a radiologist. Possibly malignant findings underwent biopsies and/or follow-up. Quantitative parameters (maximum standardized uptake value) were pooled and compared from reference lesions in each group.

RESULTS

Malignant disease was suspected in 18 of 122 tuberculosis patients and in eight of 85 sarcoidosis patients. Malignancy was finally confirmed in six patients with tuberculosis and in two patients with sarcoidosis. In one single case a malignant lung tumour had been overlooked on PET/CT. Patients were also analysed according to their age. In the patient group older than 60 years, four malignancies were confirmed in 44 tuberculosis patients and in one in 20 sarcoidosis patients, whereas in patients aged between 30 and 60 years only three of 63 tuberculosis and one of 58 sarcoidosis cases showed malignancy compared with the 18 false-positive findings on a total patient basis. The most common site of malignant disease was the chest. Besides the intrathoracic findings, two cases of malignancy were detected outside the thorax. Quantitative evaluation did not reveal any statistically significant difference between the tuberculosis and sarcoidosis groups.

CONCLUSION

Differentiation between granulomatous inflammation and malignancy is challenging with ¹⁸F-FDG-PET/CT because of a large number of false-positive findings. The highest probability of detecting coexistent malignant disease was seen in patients older than 60 years who were suffering from tuberculosis. An important feature for identification of malignant disease, especially in the assessment of intrathoracic findings, has turned out to be the CT pattern; quantitative evaluation, in contrast, seems to have little clinical value.

Diagnostic utility of 99mTc-EDDA-tricine-HYNIC-Tyr3-octreotate SPECT for differentiation of active from inactive pulmonary tuberculosis

OBJECTIVE

The current study was performed to evaluate the impact of Tc-EDDA-tricine-HYNIC-Tyr-octreotate in the differentiation of active from inactive pulmonary tuberculosis lesions.

PATIENTS AND METHODS

Ten consecutive patients (six male and four female, age range 24-83 years) with proven pulmonary tuberculosis (with a positive smear or culture) were enrolled in the study. At 120 min after injection of 740 MBq of Tc-EDDA-tricine-HYNIC-Tyr-octreotate, planar and single-photon emission computed tomography (SPECT) images of the thorax were taken. A semiquantitative evaluation of lesion and nonlesion areas was performed. The scan was repeated following the same protocol after standard treatment for tuberculosis after a negative sputum culture.

RESULTS

Semiquantitative evaluation of the lesions showed a statistically significant higher uptake before treatment in both planar and SPECT images (P=0.005 and 0.007, respectively). Lesion-to-nonlesion ratios were also higher in the pretreatment sets on both planar and SPECT images (1.4±0.2 vs. 1.19±0.15, P=0.001, for planar images and 2.32±0.55 vs. 1.32±0.32, P=0.0001, for SPECT images).

CONCLUSION

Tc-EDDA-tricine-HYNIC-Tyr-octreotate scintigraphy may help to differentiate between active and inactive pulmonary tuberculosis. SPECT imaging and semiquantitative evaluation are indispensable for increasing the diagnostic yield of this method. Larger studies are needed to corroborate our results.

Nuclear imaging: a powerful novel approach for tuberculosis

Nearly 20 years after the World Health Organization declared tuberculosis (TB) a global public health emergency, TB still remains a major global threat with 8.6 million new cases and 1.3 million deaths annually. Mycobacterium tuberculosis adapts to a quiescent physiological state, and is notable for complex interaction with the host, producing poorly-understood disease states ranging from latent infection to fully active disease. Of the approximately 2.5 billion people latently infected with M. tuberculosis, many will develop reactivation disease (relapse), years after the initial infection. While progress has been made on some fronts, the alarming spread of multidrug-resistant, extensively drug-resistant, and more recently totally-drug resistant strains is of grave concern. New tools are urgently needed for rapidly diagnosing TB, monitoring TB treatments and to allow unique insights into disease pathogenesis. Nuclear bioimaging is a powerful, noninvasive tool that can rapidly provide three-dimensional views of disease processes deep within the body and conduct noninvasive longitudinal assessments of the same patient. In this review, we discuss the application of nuclear bioimaging to TB, including the current state of the field, considerations for radioprobe development, study of TB drug pharmacokinetics in infected tissues, and areas of research and clinical needs that could be addressed by nuclear bioimaging. These technologies are an emerging field of research, overcome several fundamental limitations of current tools, and will have a broad impact on both basic research and patient care. Beyond diagnosis and monitoring disease, these technologies will also allow unique insights into understanding disease pathogenesis; and expedite bench-to-bedside translation of new therapeutics. Finally, since molecular imaging is readily available for humans, validated tracers will become valuable tools for clinical applications.

Challenges and perspectives in the diagnosis of extrapulmonary tuberculosis

Extrapulmonary tuberculosis (EPTB) accounts for a significant proportion of tuberculosis cases worldwide. Nevertheless, the diagnosis is often delayed or even missed due to insidious clinical presentation and poor performance of diagnostic tests. Culture, the classical gold standard for tuberculosis, suffers from increased technical and logistical constraints in EPTB cases. In this review the authors outline current diagnostic options for the main forms of EPTB. The authors also discuss the opportunities and challenges linked in particular to microbiological diagnostics and to the attempts to find a new gold standard test for EPTB. Finally, new biomarkers and tests currently under evaluation are hopefully on the way to introduce significant improvements in EPTB diagnosis, for which clinical suspicion will nevertheless be essential.

The tuberculous granuloma: an unsuccessful host defence mechanism providing a safety shelter for the bacteria?

One of the main features of the immune response to M. Tuberculosis is the formation of an organized structure called granuloma. It consists mainly in the recruitment at the infectious stage of macrophages, highly differentiated cells such as multinucleated giant cells, epithelioid cells and Foamy cells, all these cells being surrounded by a rim of lymphocytes. Although in the first instance the granuloma acts to constrain the infection, some bacilli can actually survive inside these structures for a long time in a dormant state. For some reasons, which are still unclear, the bacilli will reactivate in 10% of the latently infected individuals, escape the granuloma and spread throughout the body, thus giving rise to clinical disease, and are finally disseminated throughout the environment. In this review we examine the process leading to the formation of the granulomatous structures and the different cell types that have been shown to be part of this inflammatory reaction. We also discuss the different in vivo and in vitro models available to study this fascinating immune structure.