April 2 Lecture

Exam Scheduling and Attendance

• Importance of notifying the instructor if not attending the final exam includes planning for alternative assessments and ensuring fair treatment for all students. Communication channels should be clear to avoid misunderstandings.

• Class policy mandates that students must inform the instructor via email at least 24 hours in advance if they do not plan to take the exam. This allows the instructor to make arrangements for possible makeup options or to adjust the grading scheme.

• Instructor imposes a strict grading policy for those who choose not to take the exam. Failure to attend without prior notice may result in a failing grade unless valid, documented excuses are provided (e.g., a doctor’s note for medical emergencies). This encourages accountability among students.

Antigens and Histamine

• Human body reacts to allergens via histamine, leading to symptoms like itching, swelling, and respiratory issues; histamine is primarily released by mast cells and basophils in response to allergen exposure.

• Overview of common treatments for allergies includes:

• Antihistamines (e.g., loratadine, cetirizine) that block histamine receptors and alleviate symptoms like sneezing and nasal congestion.

• Decongestants like Sudafed that constrict blood vessels in the nasal passages, reducing swelling and congestion by targeting vasodilation mechanisms, but may have restrictions on sales due to potential misuse.

• Restrictions include limits on sale quantities and requirements for ID due to regulations that prevent misuse in drug manufacturing. Out-of-state residents may face additional barriers at pharmacies.

Immune System Components

• Antigen-Presenting Cells (APCs) includes macrophages and dendritic cells that capture, process, and present antigens to T cells, initiating a cascade of immune responses. They display processed antigens on MHC molecules, which is essential for T cell activation.

• Maturation and migration of dendritic cells from tissues to lymph nodes are key in establishing adaptive immunity, where T cells proliferate and differentiate into effector cells.

• T Helper Cells, particularly CD4+ T cells, release cytokines that activate B cells, cytotoxic T cells, and even phagocytes, enhancing the immune response. The differentiation of T helper cells into subsets (Th1, Th2, Th17) influences the nature of immune responses depending on the pathogen type.

• Immunoglobulin E (IgE) roles involve binding to allergens and triggering degranulation of mast cells and basophils, leading to the release of histamine. Elevated IgE levels are a hallmark of allergic diseases, indicating their systemic effects.

Immunotherapy

• Immunotherapy aims to increase immunoglobulin G (IgG) levels to provide long-term relief from allergies. This process gradually desensitizes the immune system to specific allergens through controlled exposure.

• Methods include:

• Sublingual Immunotherapy (SLIT), where allergens are placed under the tongue to promote immune tolerance and reduce IgE responses.

• Subcutaneous Immunotherapy (SCIT), which involves injecting allergen extracts in gradually increasing doses, leading to a systemic immune response that shifts toward IgG production.

• Regular monitoring is crucial to assess tolerance levels and potential side effects, ensuring that the patient can move through dosage escalations without adverse reactions.

Major Histocompatibility Complex (MHC)

• MHC Class I molecules alert the immune system about intracellular infections by presenting endogenous peptides to CD8+ cytotoxic T cells. All nucleated cells express these, which is essential for eliminating infected or tumor cells.

• MHC Class II molecules present exogenous antigens to CD4+ T helper cells, which boosts B cell production of antibodies and activates macrophages. These are predominantly expressed on professional antigen-presenting cells.

• Matching for organ transplants is critical; the degree of HLA compatibility between donor and recipient influences transplant success rates due to the risk of acute rejection from mismatched antigens. Pre-transplant testing includes tissue typing to ensure compatibility.

Transplantation and Immune Reactions

• The immune system mounts a response to foreign organs through various mechanisms, including the recognition of foreign MHCs by T-cell receptors, leading to activation of cytotoxic T cells and antibodies that target the transplanted tissue.

• Immunosuppressant medication (e.g., corticosteroids, calcineurin inhibitors) is essential to manage immune responses post-transplant by reducing T cell activation and proliferation, preventing rejection.

• Regular follow-ups and laboratory tests (e.g., blood tests for drug levels and organ function) are necessary for long-term monitoring of transplant health, allowing for timely adjustments to immunosuppressant regimens.

T Cells and Cancer

• Cytotoxic T Cells directly kill infected or malignant cells by recognizing abnormal peptide sequences presented on MHC molecules, with mechanisms like perforin and granzymes inducing apoptosis in target cells. The role of tumor-infiltrating lymphocytes (TILs) is crucial in tumor surveillance and eradication.

• Natural Killer Cells differentiate between normal and abnormal cells, targeting those with low MHC expression using a combination of activating and inhibitory receptors. This allows for rapid response to virally infected and tumor cells without prior sensitization.

• Apoptosis is a vital mechanism for maintaining health. T cells produce cytokines that can also induce apoptosis in target cells, contributing to homeostasis and the elimination of excess or harmful cells.

Autoimmune Diseases and Helper T Cells

• Helper T Cells can drive autoimmune disorders when they respond inappropriately to self-antigens, leading to chronic inflammation and tissue damage. Diverse cytokine profiles produced by Th1, Th2, or Th17 cells can exacerbate autoimmune conditions.

• HIV's targeting of Helper T Cells leads to decreased immune responses, and the depletion of these cells significantly impacts the ability to mount effective responses against infections or malignancies, highlighting the need for antiretroviral therapy to restore immune function.

Immune Memory and Vaccination

• Vaccinations stimulate both B and T cells, leading to the formation of memory cells capable of rapid response during reinfection; these cells persist long after exposure, producing a faster and stronger immune response.

• Immunoglobulin M (IgM) serves as the first line of defense during initial exposure, while IgG provides long-term immunity due to its structural adaptability.

Types of Immunity

• Active Immunity develops through natural infections or vaccinations, leading to the production of memory cells that confer long-lasting protection upon subsequent exposures.

• Passive Immunity can provide immediate but temporary protection, commonly seen in newborns receiving maternal antibodies or in clinical settings through monoclonal antibody therapies for immediate response against infections.

Innate and Adaptive Immunity

• Innate Immunity involves barriers (skin, mucous membranes) and immune cells that provide immediate, nonspecific responses to pathogens while Adaptive Immunity involves antigen-specific responses requiring prior exposure for effective action.

Pathogen Recognition and Response

• Pattern Recognition Receptors (PRRs) detect PAMPs, triggering an innate immune response through signaling pathways that lead to inflammation and recruitment of innate immune cells to the site of infection.

• The lymphatic system plays a key role in transporting leukocytes and ensuring comprehensive surveillance of peripheral tissues, while the spleen filters blood and assists in the systemic immune response.