Aged B cells alter immune regulation of allografts in mice

Immune aging: biological mechanisms, clinical symptoms, and management in lung transplant recipients

While chronologic age can be precisely defined, clinical manifestations of advanced age occur in different ways and at different rates across individuals. The observed phenotype of advanced age likely reflects a superposition of several biological aging mechanisms which have gained increasing attention as the world contends with an aging population. Even within the immune system, there are multiple age-associated biological mechanisms at play, including telomere dysfunction, epigenetic dysregulation, immune senescence programs, and mitochondrial dysfunction. These biological mechanisms have associated clinical syndromes, such as telomere dysfunction leading to short telomere syndrome (STS), and optimal patient management may require recognition of biologically based aging syndromes. Within the clinical context of lung transplantation, select immune aging mechanisms are particularly pronounced. Indeed, STS is increasingly recognized as an indication for lung transplantation. At the same time, common aging phenotypes may be evoked by the stress of transplantation because lung allografts face a potent immune response, necessitating higher levels of immune suppression and associated toxicities, relative to other solid organs. Age-associated conditions exacerbated by lung transplant include bone marrow suppression, herpes viral infections, liver cirrhosis, hypogammaglobulinemia, frailty, and cancer risk. This review aims to dissect the molecular mechanisms of immune aging and describe their clinical manifestations in the context of lung transplantation. While these mechanisms are more likely to manifest in the context of lung transplantation, this mechanism-based approach to clinical syndromes of immune aging has broad relevance to geriatric medicine.

The aging of the immune system and its implications for transplantation

By the last third of life, most mammals, including humans, exhibit a decline in immune cell numbers, immune organ structure, and immune defense of the organism, commonly known as immunosenescence. This decline leads to clinical manifestations of increased susceptibility to infections, particularly those caused by emerging and reemerging microorganisms, which can reach staggering levels-infection with SARS-CoV-2 has been 270-fold more lethal to older adults over 80 years of age, compared to their 18-39-year-old counterparts. However, while this would be expected to be beneficial to situations where hyporeactivity of the immune system may be desirable, this is not always the case. Here, we discuss the cellular and molecular underpinnings of immunosenescence as they pertain to outcomes of solid organ and hematopoietic transplantation.

Nanoparticles reduce monocytes within the lungs to improve outcomes after influenza virus infection in aged mice

Older people exhibit dysregulated innate immunity to respiratory viral infections, including influenza and SARS-CoV-2, and show an increase in morbidity and mortality. Nanoparticles are a potential practical therapeutic that could reduce exaggerated innate immune responses within the lungs during viral infection. However, such therapeutics have not been examined for effectiveness during respiratory viral infection, particular in aged hosts. Here, we employed a lethal model of influenza viral infection in vulnerable aged mice to examine the ability of biodegradable, cargo-free nanoparticles, designated ONP-302, to resolve innate immune dysfunction and improve outcomes during infection. We administered ONP-302 via i.v. injection to aged mice at day 3 after infection, when the hyperinflammatory innate immune response was already established. During infection, we found that ONP-302 treatment reduced the numbers of inflammatory monocytes within the lungs and increased their number in both the liver and spleen, without impacting viral clearance. Importantly, cargo-free nanoparticles reduced lung damage, reduced histological lung inflammation, and improved gas exchange and, ultimately, the clinical outcomes in influenza-infected aged mice. In conclusion, ONP-302 improves outcomes in influenza-infected aged mice. Thus, our study provides information concerning a practical therapeutic, which, if translated clinically, could improve disease outcomes for vulnerable older patients suffering from respiratory viral infections.

Implications of Inflammatory States on Dysfunctional Immune Responses in Aging and Obesity

Aging and obesity are two conditions characterized by chronic, low-grade inflammation. While both conditions are also associated with dysfunctional immune responses, the shared and distinct underlying mechanisms are just starting to be uncovered. In fact, recent findings have suggested that the effects of obesity on the immune system can be thought of as a state of accelerated aging. Here we propose that chronic, low-grade inflammation seen in obesity and aging is complex, affects multiple cell types, and results in an altered basal immune state. In aging, part of this altered state is the emergence of regulatory immune populations that lead to further immune dysfunction in an attempt to reduce chronic inflammation. While in obesity, part of the altered state is the effect of expanding adipose tissue on immune cell function. Thus, in this review, we compare, and contrast altered immune states in aging and obesity and discuss their potential contribution to a shared clinical problem- decreased vaccine responsiveness.

CD73 expression identifies a subset of IgM+ antigen-experienced cells with memory attributes that is T cell and CD40 signalling dependent

B-cell memory was long characterized as isotype-switched, somatically mutated and germinal centre (GC)-derived. However, it is now clear that the memory pool is a complex mixture that includes unswitched and unmutated cells. Further, expression of CD73, CD80 and CD273 has allowed the categorization of B-cell memory into multiple subsets, with combinatorial expression of the markers increasing with GC progression, isotype-switching and acquisition of somatic mutations. We have extended these findings to determine whether these markers can be used to identify IgM memory phenotypically as arising from T-dependent versus T-independent responses. We report that CD73 expression identifies a subset of antigen-experienced IgM⁺ cells that share attributes of functional B-cell memory. This subset is reduced in the spleens of T-cell-deficient and CD40-deficient mice and in mixed marrow chimeras made with mutant and wild-type marrow, the proportion of CD73⁺ IgM memory is restored in the T-cell-deficient donor compartment but not in the CD40-deficient donor compartment, indicating that CD40 ligation is involved in its generation. We also report that CD40 signalling supports optimal expression of CD73 on splenic T cells and age-associated B cells (ABCs), but not on other immune cells such as neutrophils, marginal zone B cells, peritoneal cavity B-1 B cells and regulatory T and B cells. Our data indicate that in addition to promoting GC-associated memory generation during B-cell differentiation, CD40-signalling can influence the composition of the unswitched memory B-cell pool. They also raise the possibility that a fraction of ABCs may represent T-cell-dependent IgM memory.

Aging and the immune response to organ transplantation

An increasing number of older people receive organ transplants for various end-stage conditions. Although organ transplantation is an effective therapy for older patients (i.e., older than 65 years of age), such as in end-stage renal disease, this therapy has not been optimized for older patients because of our lack of understanding of the effect of aging and the immune response to organ transplantation. Here, we provide an overview of the impact of aging on both the allograft and the recipient and its effect on the immune response to organ transplantation. We describe what has been determined to date, discuss existing gaps in our knowledge, and make suggestions on necessary future studies to optimize organ transplantation for older people.