THE ADAPTIVE IMMUNE SYSTEM

II. HUMORAL IMMUNITY

C. NATURALLY AND ARTIFICIALLY ACQUIRED ACTIVE AND PASSIVE IMMUNITY

1. Naturally Acquired Immunity

Fundamental Statements for this Learning Object:

1. Active naturally acquired immunity refers to the natural exposure to an infectious agent or other antigen by the body. The body responds by making its own antibodies.
2. There are two examples of passive naturally acquired immunity: The placental transfer of IgG from mother to fetus during pregnancy that generally lasts 4 to 6 months after birth; and The IgA and IgG found in human colostrum and milk of babies who are nursed.

LEARNING OBJECTIVES FOR THIS SECTION

Immunity may be passive or active. In passive (def) immunity, antibodies (def) made in another person or animal enter the body and the immunity is short-lived. With active (def) immunity, antigens (def) enter the body and the body responds by making its own antibodies and B-memory cells (def). In this case, immunity is longer lived although duration depends on the persistence of the antigen and the memory cells in the body.

Both passive and active immunity can be either naturally or artificially acquired. In this section we will look at naturally acquired immunity.

Naturally Acquired Immunity (def)

a. Active Naturally Acquired Immunity (def)

Active naturally acquired immunity refers to the natural exposure to an infectious agent or other antigen by the body. The body responds by making its own antibodies.

b. Passive Naturally Acquired Immunity (def)

There are two examples of passive naturally acquired immunity:

1. The placental transfer of IgG from mother to fetus during pregnancy. These antibodies generally last 4 to 6 months following birth. The immune responses reach full strength at about age 5.

2. The IgA and IgG found in human colostrum and milk of babies who are nursed. In addition to the IgA and IgG, human milk also contains:

• Oligosaccharides and mucins that adhere to bacteria and viruses to interfere with their attachment to host cells;
• Lactoferrin to bind iron and make it unavailable to most bacteria;
• B₁₂ binding protein to deprive bacteria of needed vitamin B_12;
• Bifidus factor that promotes the growth of Lactobacillus bifidus, normal flora in the gastrointestinal tract of infants that crowds out harmful bacteria;
• Fibronectin that increases the antimicrobial activity of macrophages and helps repair tissue damage from infection in the gastrointestinal tract;
• Gamma-interferon, a cytokine that enhances the activity of certain immune cells;
• Hormones and growth factors that stimulate the baby's gastrointestinal tract to mature faster and be less susceptible to infection;
• Lysozyme to break down peptidoglycan in bacterial cell walls.

According to the Centers for Disease Control and Prevention (CDC), breast-fed infants have a lower incidence of gastrointestinal infections, ear infections, atopic dermatitis, respiratory infections, urinary tract infections, meningitis, type 2 diabetes, and sudden infant death syndrome. Benefits to the mother include a decreased risk of breast cancer, ovarian cancer, and type 2 diabetes, as well stopping post-birth bleeding and temporarily suppressing ovulation. It may also be associated with a reduced risk of pediatric overweight.

Concept Map for Active and Passive Immunity

 

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Gary E. Kaiser, Ph.D.
Professor of Microbiology
The Community College of Baltimore County, Catonsville Campus
This work is licensed under a Creative Commons Attribution 4.0 International License.
Based on a work The Grapes of Staph at https://cwoer.ccbcmd.edu/science/microbiology/index_gos.html.