Immunization and Immune Testing: Principles, Types, and Applications

Immunization and Immune Testing

Artificial Methods of Immunity

Immunity can be acquired artificially through two main methods: active immunization and passive immunotherapy. These approaches are fundamental in preventing and treating infectious diseases.

• Active immunization: Administration of antigens to stimulate the patient's adaptive immune response.

• Passive immunotherapy: Transfer of antibodies from an immune individual or animal to provide immediate protection.

History of Immunization

The practice of immunization has evolved over centuries, beginning with variolation in China and advancing through scientific discoveries by Jenner and Pasteur.

• Variolation: Early method using material from smallpox scabs to induce immunity.

• Vaccination: Edward Jenner's discovery in 1796 using cowpox to protect against smallpox.

• Antibody transfer: Recognition that vaccines protect via antibody action.

Types of Vaccines

Vaccines are classified based on their composition and method of preparation. Each type has distinct advantages and limitations.

• Attenuated (modified live) vaccines: Use live pathogens with reduced virulence. Provide strong, long-lasting immunity and can confer contact immunity, but may cause mild infections or disease in susceptible individuals.

• Inactivated (killed) vaccines: Contain killed microbes or antigenic fragments. Safer but require multiple doses and often include adjuvants to enhance immune response.

• Toxoid vaccines: Use chemically or thermally modified toxins. Effective for certain bacterial diseases but require repeated doses.

• Combination vaccines: Contain antigens from several pathogens for simultaneous protection.

• Recombinant gene technology vaccines: Employ recombinant DNA techniques to improve efficacy, safety, and cost.

Vaccine Manufacture and Administration

Vaccines are mass-produced using microbial cultures, often in chicken eggs. Individuals with egg allergies must avoid certain vaccines. The CDC provides a recommended immunization schedule for different age groups.

Principal Vaccines to Prevent Human Diseases

Vaccines are available for a variety of diseases, each with specific agents, types, and methods of administration.

Vaccine	Disease Agent	Disease	Vaccine Type	Method of Administration
Hepatitis B	Hepatitis B virus	Hepatitis	Subunit	Intramuscular
Rotavirus	Rotavirus	Gastroenteritis	Attenuated, recombinant	Oral
Diphtheria, tetanus, pertussis (DTaP)	Corynebacterium diphtheriae, Clostridium tetani, Bordetella pertussis	Diphtheria, tetanus, pertussis	Toxoid, inactivated	Intramuscular
Polio	Poliovirus	Poliomyelitis	Inactivated, attenuated	Subcutaneous, oral
Influenza	Influenza virus	Flu	Inactivated, attenuated	Intramuscular, intranasal
MMR	Measles, mumps, rubella viruses	Measles, mumps, rubella	Attenuated	Subcutaneous
Varicella	Varicella-zoster virus	Chickenpox	Attenuated	Subcutaneous
HPV	Human papillomavirus	Warts, cervical cancer	Subunit	Intramuscular

Vaccine Safety

Immunization is generally safe, but may cause mild toxicity, anaphylactic shock, or residual virulence. Allegations linking vaccines to autism, diabetes, and asthma are not substantiated by research.

Passive Immunotherapy

Passive immunotherapy involves administration of antiserum containing preformed antibodies for immediate protection. Limitations include allergic reactions (serum sickness), rapid antibody degradation, and lack of long-term protection. Hybridomas are used to overcome these limitations by producing monoclonal antibodies.

Serological Tests: Principles and Applications

Serology is the study of antigen-antibody interactions in blood serum. Serological tests are used to monitor infection spread and diagnose diseases.

Precipitation Tests

Precipitation tests detect antigen-antibody complexes (precipitates) formed in optimal proportions. Immunodiffusion is a common technique.

Turbidimetric & Nephelometric Tests

These tests measure solution cloudiness to quantify proteins in serum. Turbidimetry measures transmitted light; nephelometry measures reflected light.

Agglutination Tests

Agglutination is the clumping of insoluble particles due to antibody cross-linking. Hemagglutination is used for blood typing. Titration measures antibody levels by serial dilution.

Neutralization Tests

Viral neutralization tests determine if antibodies in serum can neutralize viruses, preventing cytopathic effects in cell cultures.

Labeled Antibody Tests

These tests use antibodies linked to detectable labels, such as fluorescent dyes. Direct and indirect fluorescent antibody tests are common.

ELISA (Enzyme-Linked ImmunoSorbent Assay)

ELISA uses enzyme-labeled antibodies to detect antigens or antibodies. A color change indicates a positive result. Commonly used for serum antibody detection.

Immunoblot (Western Blot)

Immunoblot detects antibodies against multiple antigens. Proteins are separated by electrophoresis, transferred to a membrane, and detected by labeled antibodies.

Immunofiltration

Rapid ELISA using membrane filters for antibody binding, reducing assay time and simplifying administration. Used for rapid HIV testing.

Immunochromatography

Very rapid ELISA where antigen solution flows through a porous strip, producing a visible line when immune complexes encounter specific antibodies. Used in pregnancy and rapid infection tests.

Antibody-Antigen Immunological Tests and Their Uses

Test	Use
Immunofiltration	Diagnosis of syphilis, pneumococcal pneumonia
Agglutination	Blood typing, pregnancy testing, diagnosis of infections
Viral neutralization	Diagnosis of viral infections
Complement fixation	Diagnosis of measles, influenza, mumps, rubella, etc.
Direct fluorescent antibody	Diagnosis of rabies, infections of group A Streptococcus
Indirect fluorescent antibody	Diagnosis of syphilis, mononucleosis
ELISA	Pregnancy, HIV, hepatitis, Lyme disease
Immunoblot (western blot)	Confirmation of HIV, Lyme disease

Additional info: Recombinant DNA technology and monoclonal antibody production are advanced methods used to improve vaccine efficacy and immune testing accuracy.