CONICET researchers find a key mechanism that regulates the immunological response during aging

The immune system can protect the organism from different threats. This means that it can differentiate ‘the self’ (that is part of our organism) and the ‘non-self’ (what is not) such as viruses and bacteria. In addition, it can recognize what is part of our tissues but is altered, such as tumor cells. The immune system has the ability to recognize, attack and eliminate what can harm it.

However, there is a group of pathologies resulting from failures in the self-regulation of the immune system functions termed autoimmune diseases. They are more than eighty diseases in which the immune system starts reacting against its self-components including rheumatoid arthritis, multiple sclerosis, type 1 diabetes and Sjögren syndrome.

Aging of the immune system can be linked to autoimmune responses. When it is dysregulated, the immune system starts recognizing its own antigens as foreign and attacks functional tissue. This takes place when the tolerogenic circuits, which are in charge of inhibiting this type of immune response, fail.

Galectin-1: an inhibitory checkpoint of the immune system

Recently, by means of experiments conducted in animal models and biological samples from patients with Sjögren syndrome, a multidisciplinary research team of CONICET successfully demonstrated that the endogenous protein Galectin-1 (Gal1) is a key regulator of immune system homeostasis that works as an inhibitory checkpoint responsible of preventing the spontaneous occurrence of autoimmune diseases linked to aging.

The study was published in Proceedings of the National Academy of Sciences (PNAS) and was supervised by CONICET Senior researcher Gabriel Rabinovich and Associate researcher Marta Toscano. Rabinovich is the director of the ‘Immunopathology Laboratory of the Institute of Biology and Experimental Medicine’ (IBYME, CONICET) where Marta Toscano worked from 2007 until the end of 2018. Currently she is a researcher at the Dr. Arturo Oñativa Hospital in Salta.

The functions of Gal1 were identified by Rabinovich and his team more than twenty-five years ago, when he started his scientific career and worked at the Universidad Nacional de Córdoba (UNC). Since then, he has led several studies that identified the relevance of this protein in the regulation of the immune system in pathological conditions, mainly in malignant tumors as well as in infections and autoimmune diseases

For the authors, the study published in PNAS –which was part of the doctoral thesis of Verónica Martínez Allo (first author) – represents a milestone in the research on galectins, which next step will allow the development of a drug to treat autoimmune diseases.

The whole study was conducted in Argentina, at the Immunopathology Laboratory of IBYME with the collaboration of scientists from other public institutions such as the Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales (IQUIBICEN, CONICET-UBA), the Instituto de Histología y Embriología de Mendoza (IHEM, CONICET-UNCUYO) and the Hospital de Agudos Bernardino Rivadavia (GCBA), which provided patients’ samples for the studies.

Study with Gal1-deficient mice

“During the past years we provided extensive evidence showing that Gal1 functions as an immunomodulatory gear in the circuit of immune tolerance. A number of studies showed that Gal1 controls the fate and function of different immune cells, thus halting the development of autoimmunity. We found that this lectin blunts pathogenic T lymphocytes, induced tolerogenic dendritic cells and deactivated M1 macrophages (a cell type involved in the development of autoimmune diseases). However, to finally prove our major hypothesis, we proposed that Gal1 indeed functions as an inhibitory checkpoint in the control of immune response. For this, we conducted a series of studies with animal models deficient in Gal1 and analyzed the impact of this deficiency throughout life,” Rabinovich explains.

The researchers used genetically modified mice lacking Gal1 and analyzed them in the long term so as to be able to compare the diseases they developed with control mice. Thus, they managed to observe that when aging mice lacking Gal1 tend to spontaneously develop autoimmunity as they exhibit –as it happens to humans suffering from Sjögren syndrome– inflammation of salivary glands (sialadenitis) with leading CD8⁺ T pathogenic lymphocytes.

Although CD8⁺ T lymphocytes of the immune system –like TH1 and TH17 cells– can cause autoimmune diseases by damaging their own tissues, they are also essential to provide responses against viruses, bacteria and tumor cells.

“If mutant mice that lack the gene encoding Gal1 would not show a phenotype prone to autoimmunity when aging, we would have to conclude that this protein, although important was not hierarchically relevant. However, occurrence of autoimmune diseases proves that Gal1 is a crucial mediator that protect throughout life from autoimmune diseases,” the scientist stresses.

Along with the inflammation of their salivary glands and further expansion of CD8⁺ T lymphocytes, aged Gal1-deficient mice exhibited dendritic cells –those in charge of presenting the antigen to  T lymphocytes– with increased immunogenic potential and a lower frequency of regulatory T lymphocytes, whose main function within the immune system is to silence effector T lymphocytes.

Study with NOD mice

“In addition to the studies with Gal1-deficient mice, we used a model of non-obese diabetic mice (NODs) which apart from developing type 1 diabetes, they suffer from sialadenitis from week sixteen. We observed that with age, and the consequent progression of the disease, Gal1 expression decreased both in the serum and in the salivary glands, an effect that was absent mice which did not develop autoimmunity. Besides, when Gal1 was injected, tolerogenic circuits were restored and inflammation of salivary glands was reduced,” states Marta Toscano.

The study with NOD mice, in addition to link aging, decreased Gal1 and autoimmunity, encouraged scientists to develop drugs to prevent the progression of autoimmune diseases in patients based on the protein identified by Rabinovich at the beginning of the 90s.

“Apart from sialadenitis, patients with Sjögren show mouth, eye and genital dryness, a set of manifestations that implies a significant deterioration in their quality of life. So far, the available treatments seek to alleviate the symptoms. The results of these studies allowed scientists to conclude that immunomodulation with Gal1 could be a solution to this problem,” says Martínez Allo.

Studies with patient samples

Finally, thanks to the collaboration established with the Unidades de Reumatología and Anatomía Patológica del Hospital General de Agudos Bernardino Rivadavia, the researchers had access to lip biopsies from patients with Sjögren syndrome and observed that along with a greater expansion of CD8⁺T cells in the salivary gland there was a reduced expression of Gal1.

“The collection of experiments included in this work undoubtedly confirms that Gal1 hierarchically controls cellular and molecular events of the immune system and prevents the development of spontaneous age-related autoimmunity,” the researcher affirms.

“The originality of these results lies in the fact that for the first time scientists report a possible immunoregulatory role of Gal1 in the development of the Sjögren syndrome. Its scientific relevance is given, among other aspects, by the experimental approach that involved not only the use of different mouse models but also –and this is especially valuable– the observations on glandular tissue of patients,” adds Claudia Pérez Leiros, CONICET principal researcher at the IQUIBICEN and a co-author of this study.

Pérez Leiros and Vanesa Hauk, assistant researcher of the Council, provided their experience in the study of Sjögren’s syndrome. They highlighted the invitation to participate in the study they received from Rabinovich and said “it is an example of what can be done when the knowledge and skills from different research laboratories are brought together for advance of health care.”

Autoimmunity and cancer: two sides of the same coin

For many years, the research projects led by Gabriel Rabinovich have been focused on understanding how the immune system is regulated under pathological situations. Their studies have focused mainly in cancer and autoimmune diseases. Nevertheless, when looking for therapeutic solutions, both problems seem to be closely related.

“This study is focused on a better understanding of the role of Gal1 in autoimmunity but its implications and conclusions can be used for the treatment of cancer. Knowing how the immune system works against different antigens provides important tools to treat autoimmune diseases but also cancer: they are two sides of the same coin,” Toscano says.

If Gal1 deficiency can lead to development of autoimmune diseases in the elderly, its overexpression can prevent T lymphocytes from acting against pathogens or tumor cells. In this sense, according to the pathologies analyzed, therapies can seek to increase or decrease the expression of this protein.

“Gal1 is neither good nor bad itself, sometimes it plays a role as a villain when it helps a tumors or pathogens escape the immune response, but it can also act as a heroine by avoiding autoimmunity. But knowing the way the immune system is regulated gives us the possibility to manipulate it in different directions, according to the disease analyzed. Just as Gal1 expression could be pharmacologically stimulated, it could also be blocked. Furthermore, the results obtained lay the foundations for the analysis of other inflammatory conditions, such as those observed during COVID-19 triggered as a response of the SARS-CoV2 virus, responsible for this pathology”,  concludes Rabinovich.