In this task, you're given a paragraph from the research paper and your task is to generate a suitable title for the research paper based on the given paper. Under 100 words is a good title length.

We live in a hostile environment, surrounded by microbial pathogens and subject to a range of physical and chemical insults. To survive in this environment, vertebrates have evolved complex immune systems. A key element of this defence is the deployment of rapid response elements at the most probable sites of attack, which are the epithelial-cell boundaries between the body and the environment in the skin, gut and lungs. As the body's largest and most exposed interface with the environment, the skin has a central role in host defence. Before the relatively recent discovery of the immunological defences of skin, the cutaneous interface was viewed as a passive barrier between the host and the hostile environment. In the past few decades, however, it has become apparent that the mechanical aspects of epidermal defence are reinforced by a versatile and robust system of immune surveillance 1 (FIG. 1) . The crucial role of immune surveillance in maintaining homeostasis is evident from the marked increase in the frequency and severity of cutaneous malignancies and infections when immune function is limited, for example in patients with genetic and acquired immunodeficiency disorders and in those receiving immunosuppressive therapy after organ transplantation 2,3 . The regulation of skin defence mechanisms is also crucial, as inappropriate or misdirected immune activity is implicated in the pathogenesis of a large variety of acquired inflammatory skin disorders, including psoriasis, atopic and allergic contact dermatitis, lichen planus, alopecia areata and vitiligo 4-10 . The role of immune dysfunction in these conditions is emphasized by their response to immunosuppressive therapeutic interventions [11] [12] [13] [14] . Understanding the mechanisms of immune surveillance in the skin and tissue-specific immune responses also has important implications for the rational design of vaccines. To promote protective immunity, an immunization protocol must elicit not only an antigenspecific immune response, but also an effective memory response that will provide long-lived protection at the most probable sites of invasion. This applies equally to immunization against infectious organisms, which in most cases invade through the skin or the epithelia of the gastrointestinal or respiratory systems, and to the elicitation of immune responses against tumours. As we discuss, the route and means of adjuvant stimulation that is used can affect the effectiveness and utility of specific vaccine strategies. In this review, we discuss these issues in the context of recent advances in our understanding of cutaneous immune mechanisms, highlighting the interaction of The skin, as the primary interface between the body and the environment, provides the first line of defence against a broad array of microbial pathogens and trauma. In addition to its properties as a physical barrier, the skin has many active defence mechanisms. In this review, we discuss the interaction between the innate and adaptive immune systems in the skin as a model for immune function at epithelial-cell interfaces with the environment. How these mechanisms account for the robust nature of cutaneous immune surveillance and how their dysregulation drives the pathogenesis of inflammatory skin disorders and skin-based tumours are the subjects of this review.
IMMUNE SURVEILLANCE IN THE SKIN: MECHANISMS AND CLINICAL CONSEQUENCES

Adults over 65 years of age are more vulnerable to infectious disease and show poor responses to vaccination relative to those under 50. A complex set of age-related changes in the immune system is believed to be largely responsible for these defects. These changes, collectively termed immune senescence, encompass alterations in both the innate and adaptive immune systems, in the microenvironments where immune cells develop or reside, and in soluble factors that guide immune homeostasis and function. While age-related changes in primary lymphoid organs (bone marrow, and, in particular, the thymus, which involutes in the first third of life) have been long appreciated, changes affecting aging secondary lymphoid organs, and, in particular, aging lymph nodes (LNs) have been less well characterized. Over the last 20 years, LN stromal cells have emerged as key players in maintaining LN morphology and immune homeostasis, as well as in coordinating immune responses to pathogens. Here, we review recent progress in understanding the contributions of LN stromal cells to immune senescence. We discuss approaches to understand the mechanisms behind the decline in LN stromal cells and conclude by considering potential strategies to rejuvenate aging LN stroma to improve immune homeostasis, immune responses, and vaccine efficacy in the elderly.
a section of the journal Frontiers in Immunology Functional and Homeostatic impact of Age-Related Changes in Lymph node Stroma

In order to predict pathogen emergence, we must distinguish between emergence phenomena that occur via different processes. Focusing on the appearance of viral pathogens in new host species, I outline a framework that uses specific molecular characteristics to rank virus families by their expected a priori ability to complete each of three steps in the emergence process (encounter, infection, and propagation). I then discuss the degree to which the patterns expected, based solely on molecular-level structural characteristics, agree with observations regarding the ability of animal viruses to infect humans. This approach yields predictions consistent with empirical observations regarding the ability of specific viral families to infect novel host species but highlights the need for consideration of other factors, such as the ecology of host interactions and the determinants of cellular susceptibility and permissivity to specific virus groups, when trying to predict the frequency with which a virus will encounter a novel host species or the probability of propagation within a novel host species once infection has occurred.

Viral Host Jumps: Moving toward a Predictive Framework