o Physical barriers: skin, mucosal

ImmunoLinks: Bridging the Basics to the membranes

Bench - Clinical Immunology and o Chemical barriers: lysozymes,
Serology Bridging Program stomach acid, complement
Incoming 3rd Year BSMLS Students system
Reference: Christine Stevens, Clinical o Cellular defenses: neutrophils,
Immunology and Serology: A Laboratory macrophages, NK cells
Perspective (4th Edition) • No memory response

LEARNING OBJECTIVES ADAPTIVE IMMUNITY

• Specific and acquired; develops after
By the end of this session, students will be able exposure to antigen
to: • Slower to respond, but forms
• Understand the basic components of the immunologic memory
immune system • Key players:
• Differentiate innate and adaptive o B-lymphocytes: produce
immunity antibodies (humoral immunity)
• Describe antigen-antibody reactions and o T-lymphocytes: regulate and kill
serologic techniques infected cells (cell-mediated
• Identify common serologic methods immunity)
used in diagnostic testing ▪ Helper T cells (CD4+)
• Recognize the clinical relevance of ▪ Cytotoxic T cells
immunologic tests in patient care (CD8+)
• Embrace the professional role of a • Memory B and T cells enable quicker
Medical Technologist in response upon re-exposure
immunodiagnostics
CELLS OF THE IMMUNE SYSTEM
OVERVIEW OF THE IMMUNE SYSTEM • Neutrophils: first responders;
• The immune system protects the body phagocytose pathogens
from pathogens and foreign substances • Monocytes/Macrophages: antigen
• Divided into two arms: innate presentation; cytokine secretion
(nonspecific) and adaptive (specific) • Dendritic cells: professional antigen-
immunity presenting cells
• Main components: • Lymphocytes:
o Cells: lymphocytes, o B-cells: plasma cells secrete
monocytes/macrophages, antibodies
neutrophils, eosinophils, o T-cells: helper, cytotoxic, and
basophils, dendritic cells regulatory functions
o Organs: thymus, bone marrow, • NK Cells: target virally infected and
spleen, lymph nodes tumor cells
o Molecules: cytokines,
chemokines, antibodies, PRIMARY AND SECONDARY
complement proteins LYMPHOID ORGANS
• Primary (Central) Organs:
INNATE IMMUNITY o Bone Marrow: hematopoiesis,
• First line of defense: present at birth B-cell maturation
• Rapid, non-specific response to o Thymus: T-cell selection and
pathogens maturation
• Components: • Secondary (Peripheral) Organs:
o Spleen: filters blood; removes
old RBCs
 o Lymph nodes: filters lymph; site
of lymphocyte activation THE COMPLEMENT SYSTEM
o MALT/GALT: mucosa and gut- Overview:
associated lymphoid tissues • The complement system is a group of
~30 plasma proteins that enhance
ANTIGENS (complement) the ability of antibodies
• Antigen: a substance capable of eliciting and phagocytic cells to clear pathogens.
an immune response • It acts as a bridge between innate and
• Epitopes: antigenic determinants; part adaptive immunity.
recognized by antibodies
• Types of antigens: Three Activation Pathways:
o Complete antigen: can trigger 1. Classical Pathway
immune response on its own o Triggered by antigen-antibody
o Hapten: requires carrier complexes (especially IgG or
molecule to be immunogenic IgM)
• Antigens may be proteins, 2. Alternative Pathway
polysaccharides, lipids, or nucleic acids o Activated spontaneously on
pathogen surfaces (no
ANTIBODIES (IMMUNOGLOBULINS) antibodies needed)
• Y-shaped glycoproteins produced by 3. Lectin Pathway
plasma cells o Triggered by mannose-binding
• Structure: lectin (MBL) binding to
o Fab region: binds antigen microbial carbohydrates
o Fc region: determines isotype,
function Key Functions:
• Immunoglobulin classes: • Opsonization – Coats pathogens to
o IgG: most abundant, crosses enhance phagocytosis (C3b)
placenta • Chemotaxis – Attracts immune cells to
o IgM: first responder, pentameric infection site (C5a)
o IgA: mucosal immunity, found • Cell Lysis – Forms Membrane Attack
in secretions Complex (MAC) (C5b-C9)
o IgE: allergy and parasitic • Clearance of immune complexes –
defense Prevents immune complex deposition in
o IgD: B-cell receptor, function tissues
not fully known
Clinical Relevance:
ANTIGEN-ANTIBODY REACTIONS • Deficiencies in complement components
• Based on the lock and key model can lead to:
• Affinity: strength of single Fab-epitope o Recurrent infections (e.g.,
binding Neisseria spp.)
• Avidity: overall strength from multiple o Autoimmune diseases (e.g., SLE
bindings – low C3/C4 levels)
• Types of reactions: • Tests used:
o Precipitation: soluble Ag-Ab → o CH50 (total hemolytic
visible precipitate complement assay)
o Agglutination: particulate o C3 and C4 quantification via
antigen clumps nephelometry or turbidimetry
o Neutralization: antibody blocks What is Complement?
antigen function • Think of complement as a team of blood
o Complement activation: leads to proteins that help the immune system
cell lysis fight infections.
 • These proteins “complement” antibodies • Function: Punches holes in the pathogen
and immune cells—like support troops = cell lysis
arriving to help win the battle.
Clinical Note (Keep Simple)
Three Pathways – 3 Ways to Activate the • Low C3/C4 = possible autoimmune
Same System condition (like SLE)
What Starts Shortcut to • CH50 test = checks if complement
Pathway system is working
It Remember
• Some people have complement
Antibody + “Classic way –
Classical deficiencies → get frequent infections
Antigen needs antibody”
Pathogen “Alternative – no Helpful Analogy:
Alternative
surface antibody needed” “Think of complement as a domino line—no
Sugar patterns “Lectin loves matter where you start (classic, alternative,
Lectin
on bacteria sugar” or lectin), all dominoes fall toward the same
1. Classical Pathway final explosion: the MAC attack.”

Trigger: Antibody (IgM or IgG) bound to PRINCIPLES OF SEROLOGIC TESTING

antigen • Uses antigen-antibody reactions to
Think: This is the “textbook” way—it needs detect:
an antibody first o Presence of pathogens (e.g.,
Key proteins: C1, C4, C2 → activates C3 viruses, bacteria)
Example: Fighting a virus you’ve already o Exposure to infectious agents
developed antibodies for o Autoimmune diseases
• Can be qualitative (negative/positive) or
2. Alternative Pathway quantitative (titer levels)
• Based on visual or measurable reactions
Trigger: Pathogen’s surface—no antibody (color change, clumping, fluorescence)
needed
Think: Fast and automatic—innate COMMON SEROLOGIC METHODS
immunity kicks in 1. ELISA (Enzyme-Linked
Key proteins: Factor B, D, and properdin Immunosorbent Assay)
Example: First time infection with a bacteria o Highly sensitive; detects Ag or
Ab
3. Lectin Pathway o Enzyme-substrate → color
change
Trigger: Mannose (a sugar) on microbial o Formats: direct, indirect,
surfaces sandwich
Think: Uses mannose-binding lectin (MBL) 2. Latex Agglutination
instead of antibodies o Latex beads coated with
Shares same steps as classical after antibodies or antigens
activation o Clumping indicates positive
Example: Body recognizes sugar coating on reaction
fungus or bacteria 3. Immunofluorescence (IFA)
o Fluorescent dye-labeled
All 3 Pathways Lead to… antibodies
o Used for ANA, Treponema
C3 Activation → C5 Activation → MAC detection
(Membrane Attack Complex) 4. Western Blot
• MAC = C5b + C6 + C7 + C8 + C9 o Separates proteins via gel
electrophoresis
 o Transfer → probing with • Professionalism:
specific antibodies o Timely, accurate reporting
o Confirmatory test for HIV, o Honesty in data interpretation
Lyme disease o Continuous learning and
competency assessment
QUALITY CONTROL IN SEROLOGY
• Specimen considerations: COURSE PREVIEW (3rd Year
o Correct collection tube (e.g., red Immuno/Serology)
top) • Major Topics:
o Storage: avoid hemolysis; o Immunologic Disorders
refrigerate if delay in testing o Advanced Serologic Testing
• Reagent quality: o Immunoassays and Automation
o Check expiration date o Flow Cytometry Introduction
o Store per manufacturer o Molecular Immunology (PCR
instructions basics)
• Controls: • Laboratory Focus:
o Run positive and negative o Hands-on serologic testing
controls with each batch o Quality control
• Common errors: o Case analysis and diagnostic
o Cross-reactivity interpretation
o Improper pipetting
o Contamination SUMMARY & CLOSING
• Immunology is a dynamic and essential
CLINICAL APPLICATIONS foundation for disease diagnosis
• HIV Testing: • Serologic techniques are tools that
o ELISA → Western Blot reveal hidden conditions
confirmation • As Medical Technologists, you bridge
• Hepatitis Testing: science and patient care
o HBV: HBsAg, Anti-HBs, Anti-
HBc “The immune system is not just a
o HCV: anti-HCV via ELISA, defense—it’s a story of balance,
NAT for confirmation
• Syphilis Testing: recognition, and precision. As future
o Non-treponemal: VDRL, RPR MLS professionals, you are its
o Treponemal: FTA-ABS, TP-PA storytellers in the lab.”
• Autoimmune Disorders:
o ANA for SLE
Prepared by:
o RF for rheumatoid arthritis
o Anti-dsDNA, Anti-CCP, Anti- AL-HADAD D. KALON, RMT, MLS (ASCPi)
Smith SMLS, Faculty

ETHICS AND RESPONSIBILITY

• Confidentiality: Protect patient identity
and data
• Informed Consent: Ensure proper
authorization for tests
• Biosafety Practices:
o Always wear PPE
o Proper disposal of biohazards