Point for Practice

Using your knowledge of wound healing, identify strategies for promoting tissue repair in older adults.

Ageing changes in the immune system

The immune system reaches its functional peak around the period of puberty, after which it reduces its capacity over a person’s lifespan by between 5% and 30% (Carter and Pottinger, 2001). Despite ageing changes, the immune system continues to maintain its defensive function even in very old adults. However, some, but not all, aspects of the immune system do decline with advancing age (Ginaldi and Sternberg, 2003). Therefore, it should not come as a surprise that very old people are more likely to die of infectious diseases including pneumonia, influenza and gastro-enteritis among others. This can be directly linked to the ageing changes in the immune system as it no longer protects to the same level when compared with younger people (Ginaldi and Sternberg, 2003). Not only are older people at greater risk of dying from infections, but they also respond differently to the presence of microorganisms. Infection can occur in older people on exposure to reduced number of microorganisms as compared with younger adults. Older people may also respond differently to infections when compared with younger people. Urinary tract infection (UTI) is a good example where a different response occurs in older adults who commonly present with signs of confusion prior to signs of pyrexia. Symptoms of infection may also be masked or mistaken for other diseases, or symptoms may appear less severe (Carter and Pottinger, 2001).

Other factors can impact on older people’s ability to combat infection and they should also be considered. These include taking medications that can increase the risk of infection. Examples of these drugs include steroids and anti-inflammatory medications both of which reduce the inflammatory response. Older people are at risk from long-term conditions such as diabetes and chronic obstructive pulmonary disease (COPD) and their presence can also increase the likelihood of infection.

Changes in the immune system due to the ageing process are called immuno-senescence. There seems to be a significant reduction in the immune system’s ability to respond efficiently and changes occur both in the innate elements of the immune system and the adaptive elements of the system (Linton, 2007). The changes in innate immunity presents as a low-grade inflammatory status while the adaptive immunity is characterised by an exhaustion of clone-specific antibodies (Ginaldi et al., 2007). In addition, older people are also more at risk of cancers and autoimmune diseases due to increased susceptibility to infection. Older people not only have a reduction in the level of protection against invading pathogens, but they also have slower and less dramatic hypersensitivity reactions (Linton, 2007).

Changes in the thymus

Atrophy of the thymus occurs naturally and progressively with ageing (Ginaldi et al., 2007). With age, productivity of the thymus decreases and it produces fewer new T cells. The thymus decreases in size and contains fewer thymocytes and epithelial cells. Along with the structural decline of the thymus, thymic productivity declines steadily (Hakim and Gress, 2007). The major impact of this ageing change is on the T cells (Meiner and Lueckenotte, 2006). The atrophying thymus affects the production of naïve or virgin T cells so that a decreased number are produced. Accompanying the decrease in naïve T cells are an increased number of memory cells, increased production of cytokines as well as a collection of activated effector cells that occupy T cell space but are unable to work fully as T cells.

T cell function

Cell-mediated immunity decreases with age; lymphocyte function diminishes and is linked to a decline in T cell function. The T cells themselves are also less able to respond and reproduce after exposure to an antigen (Meiner and Lueckenotte, 2006). Fewer T cells are available to respond to the presence of new antigens due to the involution of the thymus. As a result of this, most T cells in older adults have previously been exposed to an antigen (Linton, 2007). The mass of memory T cells diminish and the availability of naïve T cells is also severely reduced leading to a diminished range of available T cells to combat infection.

Basal levels of immune function are maintained although the ability of the immune system to cope with major immunological stressors including chronic or acute infections diminishes (Ginaldi and Sternberg, 2003). However, immune competence may well be severely limited by the decline in naïve T cell numbers (Hakim and Gress, 2007). Older adults have a greater percentage of memory T cells than naïve T cells, both of which have a diminished functional capacity. The immune system in older people therefore responds more slowly to the presence of new and previously encountered infectious agents (Graham et al., 2006).

B cell function

Humoral immunity in older people is affected by B cells producing less immunoglobulin (antibodies) although they do maintain their numbers. However, there is a related decline in hypersensitivity or allergic reactions (Meiner and Lueckenotte, 2006). There is also a loss in the diversity and affinity of immunoglobulin resulting from disruption to lymphocyte production in the lymph nodes (Aw et al., 2007). There is a corresponding decline in the production of antibodies which are crucial to both innate and adaptive immunity (Castle, 2000 in Graham et al., 2006). There are two particular problems resulting from the changes in humoral (specific) immunity in older people. First, responses to antibodies are reduced, the response to vaccines is of a lower titre, the period of protective immunity is shorter and the antibody affinity is lower. Second, there is an increase in the production of autoantibodies, which may lead to the development of autoimmune disorders. The decline in B cell populations contributes to a gradual shift towards B cell populations and responses dominated by antigen experienced memory B cells (Hakim and Gress, 2007).

A primary immune response is where a person is exposed to a particular antigen for the first time. They often succumb to illness while they identify the specific antigen and mount an appropriate immune response. This immunity is not thought to be affected with age (Meiner and Lueckenotte, 2006).

A secondary immune response is where the person is exposed to a previously encountered antigen. Here, they mount a rapid and violent response to the antigen due to the presence and action of memory cells. The overall immune response is generally rapid and violent enough to remove the offending antigen before the person succumbs to illness. This immune response is not as effective in older adults due to the reasons outlined earlier.

Natural killer cells

There does not seem to be a decrease in NK cell activity (Meiner and Lueckenotte, 2006). However, the total number of NK cells increase with advancing age as does the number of NK cells expressing NK receptors (Linton, 2007). However, the function of the NK cells seems to be depressed in older people (Aw et al., 2007). The production of cytokines by activated NK cells is also impaired. In relation to humoral immunity, there is an increase in autoantibodies even though vaccine response diminishes (Linton, 2007). Circulating NK cells increase in the peripheral blood of healthy people who are over 70 years of age when compared to young or middle-aged people. This increase in NK cells in the peripheral blood is linked to a decrease in the number of T cells. The reduced number of T cells decreases cytolysis (destruction of cells) which appears to be compensated for by an increase in the number of NK cells (Ginaldi et al., 2007).

Inflammatory process

There is no doubt that as we age we are increasingly at risk of developing a number of inflammatory disorders including diabetes, sarcopenia and atherosclerosis. The increasing risk of inflammatory disorders in old age may be linked to the fact that people are living much longer than their ancestors and the immune system has to function and protect the individual for a far greater length of time than before (Ginaldi et al., 2007). Therefore, older people are exposed to many years of antigenic stressors. This chronic antigenic stress and subsequent inflammatory burden have a major impact on survival and frailty. The lengthy period of activity of the immune system leads to inflammation which over time becomes chronic and goes on to damage several organs in the body. The process of chronic inflammation that is peculiarly linked to the ageing individual is called inflammaging. The process of inflammaging seems to be under genetic control and has a deleterious effect on longevity. The ageing immune system becomes less able to respond to the effects of new antigens on the one hand, but on the other hand becomes more prone to chronic inflammatory reactions. This pro-inflammatory condition is referred to as chronic antigenic overload (Ginaldi et al., 2007).

As ageing occurs, the production of pro-inflammatory cytokines by macrophages and fibroblasts increases. As compared to younger adults, middle-aged and older adults typically have higher levels of cytokines with pro-inflammatory functions circulating in the blood (Graham et al., 2006). The body is therefore continually challenged by antigens resulting in the production and release of inflammatory mediators which then trigger associated inflammatory diseases (Aw et al., 2007). Inflammatory processes are part of the non-specific immune response. This is evident when acute infection or tissue damage is present and inflammatory processes are triggered in order to isolate the affected area and initiate body responses to begin removal of the offending antigen. The inflammatory response includes increasing the flow of blood to and from the area of inflammation and movement of cells and fluids from blood vessels to the site of inflammation, both of which contribute to redness, heat, swelling and discomfort. Fever can also be associated with inflammation due to the release of pyrogens from white blood cells or from bacterial toxins. Pyrogens are fever-inducing substances.

Pro-inflammatory cytokine proteins enhance communication between the cells that have a central role in the inflammatory process. In older adults, wound healing may be impaired due to reduced ability of macrophages to produce pro-inflammatory cytokines in the local environment.

Chronic inflammation has been described as a dangerous disruption of homeostasis and increases the likelihood of developing long-term conditions such as atherosclerosis, cardiovascular disease, cancer, osteoporosis and rheumatoid arthritis (Graham et al., 2006).

The innate immune system is supported by a number of different factors which are outlined as follows. These supporting factors become less effective with advancing age.

Nutrition

Older people have an increased risk of developing nosocomial infections as a result of under-nutrition, unintentional weight loss and low serum albumin levels (Meiner and Lueckenotte, 2006). Older people who have nutritional deficiencies have considerable reductions in delayed cutaneous hypersensitivity also known as type IV hypersensitivity reactions. A significant deficiency of protein and energy nutrients leads to major alterations in immune function (Carter and Pottinger, 2001). These alterations include impairment of maturing T cells. Serum immunoglobulin G and immunoglobulin M (antibodies) levels are also diminished. There is a decline in the number of phagocytic cells and they no longer function effectively. This allows microorganisms to develop and reproduce more readily. Complement activity is also reduced (Linton, 2007). Complement refers to a group of plasma proteins which, when activated, leads to an action known as ‘membrane attack complex’. This action results in the destruction of the invading microorganism.

Complement activity supports the body’s defence systems. Overall, these changes lead to an increased risk of infection.

If iron and trace element deficiency are present, there is compromise of lymphocyte and granulocyte functions. Low iron levels decrease the number of circulating T cells and also contribute to a decline in the function of neutrophils, macrophages, B cells and T cells. The functional decline of these defence cells can lead to a delay in the body’s response to antigens.

The trace elements zinc, selenium and copper are all necessary for a healthy immune system (Meiner and Lueckenotte, 2006). If zinc deficiency becomes chronic, it may result in impaired cell-mediated immunity, wound healing and protein synthesis (Gorczynski and Terzioglu, 2008). The trace elements selenium and copper also improve humoral immunity. The presence of selenium seems to be implicated in protecting the body against malignancy.

Vitamin deficiencies also affect immune function. Vitamins A, C, D, E and B6 are important for cell-mediated immunity while vitamin C supplements may improve the ability of lymphocytes to respond when required. If dietary supplements of A, C and E are taken, they can improve cell-mediated immunity in older people (Meiner and Lueckenotte, 2006). If there is a deficiency in vitamin E, there appears to be a reduction in the function of NK cells which are essential for immunity against both tumours and viruses (Gorczynski and Terzioglu, 2008).

Unsaturated fats may impair immune function and increase the possibility of the development of autoimmune disease. Polyunsaturated fats have been linked to a decline in T cell function (Meiner and Lueckenotte, 2006).

Related posts:

Controlling Body Temperature Theories of Ageing Final Thoughts on Ageing Eating and Drinking Eliminating Breathing

Stay updated, free articles. Join our Telegram channel

Join