Immunopharmacology
1. Immunology Fundamentals
Immunology is the study of our protection from foreign macromolecules or invading organisms and our responses to them.
Foreign macromolecules, called antigens, include virus proteins, worms, parasites, and any substance that should not normally be present in the body. The defensive mechanism that provides protection against infectious diseases caused by these foreign substances is called immunity.
When foreign substances are introduced into the body, they trigger an immune response, where immune cells and molecules interact with the foreign invader to destroy or neutralize it.
Key Concept:
The immune system must distinguish between "self" (the body's own cells and molecules) and "non-self" (foreign invaders) to mount an appropriate response without attacking the body's own tissues.
2. Immune System Components
Two Main Branches of the Immune System:
The Innate Immune System
A general, non-specific response to anything other than recognized "self" cells. It provides the first line of defense and includes:
- Anatomic barriers: Intact skin, cilia, mucous membranes
- Physiological barriers: Temperature, saliva, lysozyme, sebum, pH, reflexes
- Phagocytic barriers: Cells that engulf and destroy invaders (e.g., macrophages, neutrophils)
- Inflammatory barriers: Redness, swelling, heat, and pain responses
The Adaptive Immune System
A specific counter-assault against a "known foreign" invader that has been previously recognized. Key features include:
- Antigen specificity: Recognizes specific antigens (via lymphocytes: B cells, T cells, NK cells)
- Diversity: Can recognize a vast array of different antigens
- Immunological memory: Remembers previous encounters for faster response upon re-exposure
- Self/nonself recognition: Distinguishes between self and foreign antigens
3. Antigens and Antibodies
Antigens
Antigen: A substance that, when introduced into the body, stimulates the production of an antibody.
Antigens are typically organic compounds - proteins, polysaccharides, or glycolipids. Structurally, antigens consist of two parts:
- Hapten: A small molecule that can elicit an immune response only when attached to a larger carrier molecule
- Carrier: A larger molecule (often a protein) that helps present the hapten to the immune system
Examples of antigens include toxins, bacteria, foreign blood cells, microorganisms, allergens, and viruses.
Clinical Note: Hapten Inhibition
Sometimes, a small-molecule hapten can block the immune response to the hapten-carrier complex by preventing it from binding to antibodies. This phenomenon is called hapten inhibition and has implications for drug design and allergy treatments.
Antibodies (Immunoglobulins)
Antibodies are gamma globulins or immunoglobulins produced in serum upon exposure to antigens. Chemically, they are glycoproteins containing:
- Two identical heavy chains
- Two identical light chains
- Disulfide bonds joining the chains together
Antibody structure includes two main regions:
- Fab (Fragment antigen-binding): Binds to antigens
- Fc (Fragment crystallizable): Mediates effector functions (complement activation, binding to Fc receptors)
Types & Characteristics of Antibodies:
There are five main classes of antibodies (immunoglobulins):
- IgG: Most abundant in blood, crosses placenta, secondary immune response
- IgM: First antibody produced, pentameric structure, primary immune response
- IgA: Found in secretions (mucosal immunity), dimeric structure
- IgE: Involved in allergic reactions and parasitic infections
- IgD: Function not fully understood, found on surface of B cells
4. Lymphocytes: B Cells and T Cells
Lymphocytes are specialized leukocytes that form the core of the adaptive immune system. They are divided into two main types:
B Cells
B cells are essential components of the adaptive immune system with several critical functions:
- Precursors of plasma cells that produce antibodies
- Can bind specifically to antigens via their B cell receptors (BCRs)
- Produce antibodies against specific antigens
- Function as antigen-presenting cells (APCs) to T cells
- Develop into memory B cells after antigen activation for long-term immunity
T Cells
T cells recognize "non-self" targets (pathogens) only after antigens are presented in combination with "self" receptors called Major Histocompatibility Complex (MHC) molecules.
Types of T Cells:
- Cytotoxic T cells (CD8+): Recognize antigens coupled to Class I MHC molecules; directly kill infected or abnormal cells
- Helper T cells (CD4+): Recognize antigens coupled to Class II MHC molecules; regulate immune responses by secreting cytokines
- Regulatory T cells (Tregs): Suppress immune responses to prevent autoimmunity
- Memory T cells: Provide long-term immunity against previously encountered pathogens
Pharmacological Relevance:
Understanding lymphocyte function is crucial for developing immunomodulatory drugs, vaccines, and therapies for autoimmune diseases, allergies, and cancer immunotherapies.
5. Organ Transplantation
Organ Transplantation: Replacement of a diseased vital organ with a viable organ from a living or cadaver donor.
Solid organ transplantation has become the therapy of choice for many patients with end-organ failure (heart, liver, lung, and kidney disease).
Classification of Transplantation:
Solid Organ Transplantation
Life-saving transplantation: No alternative life-sustaining method available (e.g., heart, heart-lung, lung, liver).
Non-life-saving transplantation: Alternative life-sustaining methods available, but transplantation improves quality of life or long-term survival (e.g., kidney, pancreas, cornea).
Hematopoietic Stem Cell (Bone Marrow) Transplantation
Used mainly for hematological malignancies (leukemias, lymphomas) or aplastic anemia. This procedure replaces the recipient's bone marrow with healthy stem cells.
Graft Rejection
The body's immune system recognizes the allograft (transplanted organ) as foreign and initiates an immune response to destroy it. The degree of rejection depends on genetic similarities between donor and recipient.
| Type of Rejection | Time Frame | Mechanism | Treatment |
|---|---|---|---|
| Hyperacute | Minutes to hours | Preformed antibodies against donor antigens (ABO mismatch) | No adequate treatment; graft must be removed |
| Acute | Days to months | Mainly T-cell mediated (cellular rejection) | Reversible with steroids or antibody therapy |
| Chronic | Months to years | Thought to be B-cell mediated (antibody) | No adequate treatment available |
6. Immunosuppressants
Immunosuppressants: Agents that suppress or reduce the strength of the body's immune system.
Most immunosuppressants act during the induction phase of the immunological response. Their primary applications include:
- Prevention of graft rejection in organ transplantation
- Treatment of autoimmune disorders (e.g., rheumatoid arthritis, lupus, psoriasis)
- Management of hemolytic diseases
Classification of Immunosuppressants:
1. Calcineurin Inhibitors
Examples: Cyclosporine, Tacrolimus
Mechanism: Inhibit T-cell activation by blocking calcineurin, preventing IL-2 production
2. Antiproliferative Agents
Examples: Azathioprine, Mycophenolate Mofetil
Mechanism: Inhibit DNA synthesis and lymphocyte proliferation
3. mTOR Inhibitors
Examples: Sirolimus, Everolimus
Mechanism: Block mTOR pathway, inhibiting T-cell proliferation
4. Corticosteroids
Examples: Prednisone, Methylprednisolone
Mechanism: Broad anti-inflammatory effects; inhibit cytokine production
5. Biologic Agents
Examples: Monoclonal antibodies (Basiliximab, Daclizumab, Alemtuzumab)
Mechanism: Target specific immune cells or cytokines
Clinical Considerations:
Immunosuppressant therapy requires careful monitoring due to:
- Increased risk of infections (opportunistic pathogens)
- Potential for drug toxicity (nephrotoxicity, hepatotoxicity)
- Risk of malignancies (particularly lymphoproliferative disorders)
- Metabolic side effects (hyperglycemia, dyslipidemia, hypertension)
7. Immunostimulants and Vaccines
Immunostimulants enhance the body's immune response. The most common form of immunostimulation is vaccination, which can be active or passive.
Active Immunization (Vaccines)
Active immunization involves administering antigens to stimulate the production of antibodies and memory cells. Vaccine types include:
| Vaccine Type | Examples | Characteristics |
|---|---|---|
| Live attenuated | Measles, Mumps, Rubella (MMR), BCG, Oral polio | Weakened pathogen; generally single dose; contraindicated in immunocompromised |
| Inactivated/killed | Influenza, Pertussis, Typhoid, Rabies | Dead pathogen; requires multiple doses; safer for immunocompromised |
| Subunit/conjugate | Hepatitis B, Haemophilus influenzae type b (Hib) | Purified antigens; often require adjuvants |
| Toxoid | Tetanus, Diphtheria | Inactivated toxins; stimulate antitoxin antibodies |
| mRNA/DNA vaccines | COVID-19 mRNA vaccines | Newer technology; provide genetic instructions for antigen production |
Vaccination Schedule Principles:
- Live attenuated vaccines: Generally single dose (except oral polio and typhoid: 3 doses)
- Two live virus vaccines: Give simultaneously at different sites or with ≥3-week interval
- Inactivated vaccines: Require primary series plus booster doses
- Toxoid vaccines: More immunogenic when adsorbed onto adjuvants (e.g., aluminum hydroxide)
Passive Immunization
Passive immunization provides immediate, short-term protection by administering pre-formed antibodies:
- Immunoglobulins: Antibodies of human origin (e.g., Hepatitis B immune globulin, Tetanus immune globulin)
- Antisera: Antibodies prepared in animals (higher risk of serum sickness; replaced by immunoglobulins when possible)
Vaccine Side Effects and Contraindications:
Common side effects: Discomfort at injection site, mild fever, malaise
Serious reactions: Rare (e.g., anaphylaxis, Guillain-Barré syndrome)
Contraindications: Acute illness, pregnancy (for live vaccines), immunosuppression, known hypersensitivity to vaccine components
8. Expanded Programme on Immunization (EPI)
The World Health Organization (WHO) launched the Expanded Programme on Immunization (EPI) in May 1974 to protect children worldwide against six vaccine-preventable diseases:
- Tuberculosis
- Diphtheria
- Pertussis (Whooping cough)
- Tetanus
- Poliomyelitis
- Measles
Hepatitis B was added to the EPI schedule by many countries in 1992-93.
EPI in Bangladesh
Bangladesh formally launched EPI on April 7, 1979, and adopted the goal of 'Universal Child Immunization' (UCI) in 1985.
Progress and Challenges:
- Vaccination rate increased from 76.0% (1995) to 94.2% (recent data)
- Significant contribution to achieving Millennium Development Goal 4: Reducing Child Mortality
- Current target: 90% national coverage, 85% in all districts
- Current status: 85.6% national coverage (as of latest data)
WHO EPI Immunization Schedule for Infants
| Vaccine | Primary Schedule | Booster |
|---|---|---|
| BCG (Tuberculosis) | At birth | None |
| Oral Polio Vaccine (OPV) | At birth, 6, 10, 14 weeks | None |
| Pentavalent (DTP-HepB-Hib) | 6, 10, 14 weeks | None |
| PCV (Pneumococcal) | 6, 10, 14 weeks | 9 months |
| Measles-Rubella (MR) | 9 months | 15 months |
9. Laboratory Techniques in Immunology
Methods Using Antibodies
Quantitation of Antigens by Immunoassays
Radioimmunoassay (RIA): Uses radioisotope-labeled antibodies/antigens; highly sensitive but requires special handling due to radioactivity.
Enzyme-Linked Immunosorbent Assay (ELISA): Uses enzyme-labeled antibodies; colorimetric detection; widely used in clinical and research settings.
Purification and Identification of Proteins
Immunoprecipitation: Uses antibody-coated beads to isolate specific antigens from mixtures.
Western Blotting: Separates proteins by molecular weight (SDS-PAGE), transfers to membrane, detects with specific antibodies.
Affinity Chromatography: Uses antibody-coated columns to purify specific antigens.
Labeling and Detection in Cells and Tissues
Flow Cytometry and FACS: Analyzes cell surface/intracellular molecules using fluorescently labeled antibodies; can sort cells based on markers.
Immunofluorescence: Uses fluorescent antibodies to visualize antigens in cells/tissues.
Immunohistochemistry: Uses enzyme-labeled antibodies to detect antigens in tissue sections.
Analysis of Gene Structure and Expression
Southern Blotting
Used to analyze DNA structure. DNA is digested with restriction enzymes, separated by gel electrophoresis, transferred to membrane, and hybridized with labeled DNA probes.
Northern Blotting
Used to analyze RNA expression. RNA is separated by gel electrophoresis, transferred to membrane, and hybridized with labeled DNA probes.
Polymerase Chain Reaction (PCR)
Amplifies specific DNA sequences. Key steps:
- Denaturation: Heat (94-98°C) separates DNA strands
- Annealing: Cooler temperature (50-65°C) allows primers to bind
- Extension: DNA polymerase (e.g., Taq polymerase) synthesizes new strands (72°C)
Applications: Diagnosis of infections, genetic testing, forensic analysis, research.
10. Serology and AIDS
Serology
Serology: The study of antibodies and their reactions with antigens in serum.
Serum is the fluid remaining after blood clots. Antibody concentration (titer) is measured by serial dilutions until no binding is observed.
Coomb's Test (Antiglobulin Test)
Detects antibodies bound to red blood cells (RBCs). Uses anti-human antibodies to agglutinate RBCs with bound antibodies.
Clinical Applications:
- Blood transfusion cross-matching
- Antenatal screening for atypical antibodies in pregnant women
- Diagnosis of immune-mediated hemolytic anemias
AIDS (Acquired Immunodeficiency Syndrome)
HIV/AIDS is caused by human immunodeficiency virus (HIV) infection, leading to progressive immune system failure.
Key Facts:
- Transmission: Unprotected sex, contaminated blood, needles, mother-to-child
- Global impact (2015 data): 36.7 million people living with HIV; 1.1 million deaths
- Treatment: No cure or vaccine; antiretroviral therapy (ART) can control infection
- Without treatment: Average survival 11 years after infection
New Developments in HIV Treatment
- Berlin Patient (Timothy Ray Brown): First person cured of HIV after bone marrow transplant from donor with CCR5 delta-32 mutation (HIV-resistant cells)
- Gene editing: CRISPR/Cas9 used to delete HIV from T cells (Temple University, 2016)
- Cell-based therapies: Experimental approaches using modified immune cells
Pharmacist's Role in HIV Management:
Pharmacists play crucial roles in HIV care through:
- Medication therapy management for ART regimens
- Managing drug interactions and side effects
- Providing adherence counseling
- Pre-exposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP) counseling
- Vaccination guidance for immunocompromised patients
References & Further Reading
1. Abbas, A. K., Lichtman, A. H., & Pillai, S. (2020). Cellular and Molecular Immunology. Elsevier.
2. Brunton, L. L., Hilal-Dandan, R., & Knollmann, B. C. (2017). Goodman & Gilman's: The Pharmacological Basis of Therapeutics. McGraw-Hill Education.
3. WHO Expanded Programme on Immunization. (2023). Immunization Coverage. World Health Organization.
4. Danziger-Isakov, L. (2019). Immunizations in Solid Organ Transplantation. American Journal of Transplantation.
5. Janeway, C. A., Travers, P., Walport, M., & Shlomchik, M. J. (2001). Immunobiology: The Immune System in Health and Disease. Garland Science.