Immunodeficiency disorders - Secondary: Nursing

Secondary immunodeficiencies are acquired disorders that occur as a result of some extrinsic factor affecting the immune system.

Let’s start with some immune system physiology. The immune system consists of white blood cells that protect us from pathogens, like viruses, bacteria, and fungi; but, also, foreign substances, such as toxins and chemicals, and destroy abnormal cells, such as those that might develop into cancer.

Now, the immune system consists of two main branches: innate immunity and adaptive immunity. The innate immune response involves non-specific defense mechanisms, meaning they don’t differentiate one pathogen from another. These include complement proteins and cells like phagocytes and natural killers; as well as dendritic cells, which activate the adaptive immune response. The adaptive immune response is highly specific, meaning that it recognizes different pathogens and is mediated by cells called lymphocytes, which include T and B cells.

T cells can be further divided into CD4+ and CD8+ T cells. CD4+ T cells are also known as T helper cells, because they interact with dendritic cells, and in turn help activate the rest of the lymphocytes. On the other hand, CD8+ T cells, also known as cytotoxic T cells, are in charge of cell-mediated immunity, where they attack abnormal cells. Finally, B cells mediate a specific adaptive response, called humoral immunity, by secreting antibodies that bind to and destroy extracellular antigens. These antibodies can be classified into several classes, including IgA, IgG, IgM, and IgE.

Now, there are several causes of secondary immunodeficiency, including calorie and protein malnutrition; adverse environmental conditions, like UV light, extreme cold, or high altitude; surgery and trauma; and medications, such as glucocorticoids, chemotherapy, and immunosuppressive agents used to treat autoimmune disorders or to prevent organ transplant rejection.

Additionally, secondary immunodeficiency can be also caused by several medical conditions, including various types of cancer, specifically hematological malignancies, like leukemia, lymphoma, and multiple myeloma; metabolic disorders, like diabetes mellitus or chronic kidney disease; and genetic conditions, such as Down syndrome or trisomy 21. Finally, other causes include trauma, surgery, as well as infectious diseases, the most common of which is acquired immunodeficiency syndrome, or AIDS, resulting from HIV infection.

On the other hand, risk factors for secondary immunodeficiencies include engaging in high-risk sexual behaviors, since that can increase the risk of contracting an HIV infection; undergoing chemotherapy or immunosuppresive treament; as well as being critically ill or hospitalized for a long period of time. Additionally, newborns and elderly clients are especially susceptible to immunodeficiency, since they naturally have a decreased immune response to pathogens.

Secondary immunodeficiencies affect the immune system in different ways, but what they all have in common is that they leave clients more vulnerable to developing frequent infections, as well as unusual complications from infections that a healthy immune system would typically be able to fend off. Conditions that lead to weakened mucosal barriers, such as malnutrition and burns, can increase the risk of diarrhea and skin or respiratory tract infections. In contrast, those that affect cellular immunity, such as HIV, and genetic and metabolic diseases reduce the overall effectiveness of the immune response, thereby increasing the risk of all sorts of infections. Finally, trauma and some surgical procedures, like a splenectomy, can affect organs involved in the immune system, thereby increasing the risk of infection with encapsulated bacteria like Streptococcus pneumoniae and Haemophilus influenzae.

Now, there are also certain infections that occur more frequently or have more severe symptoms in people who are immunocompromised, and these are called opportunistic infections. For example, most people infected with toxoplasma, a type of parasite, don’t have symptoms; but in people with immunodeficiency it can cause encephalitis.