Topic 1   Overview of Immunity

Introduction

The animal body with its warmth, moisture, cells, and rich supplies of nutrients represents an ideal habitat for the growth of bacteria, fungi, viruses, and other parasites. If the body was not actively defended, it would be rapidly invaded by many different organisms.  This lesson will introduce you to mechanisms which allow our bodies to survive and fight back.  Among new terms introduced in this lesson is immunity which refers to all the mechanisms used by the body as protection against environmental agents that are foreign to the body.   Such immunity may be innate or acquired.   We will learn that major functions of the immune system are: homeostasis, defense and surveillance.  Immunological defense mechanisms differentiate between those molecules that are intrinsic to the organism, or “self” and those molecules that are foreign, or “non-self.” These defense mechanisms then attempt to eliminate the foreign molecules.   The immune surveillance mechanisms scan the molecules of the organism to detect and eliminate changes or modifications to “self." Thus, homeostasis, the steady state of an organism with respect to its environment, is controlled by its immunological defense and surveillance functions.  In this lesson you will also be introduced to the major biological chemical and physical components of an organism’s internal environment  that play a role in preserving  the steady state of the organism.  A brief historical survey describing the origins of immunology and its involvement in our understanding of immunity is presented as an introduction to the lesson.

Objectives

On completion of this section and the required readings, you should be able to:

n  identify and explain three functions of the immune system;

n  distinguish between innate immunity and acquired immunity;

n  discuss how the clonal selective theory explains the immune systems’s ability to recognize millions of antigens;

n  describe the basic structural and functional components of the immune system.

Required Reading

Please refer to the textbook key for specific readings for this section.

 

P Key Terms

•    humoral immunity •    cell mediated immunity •    clonal selection •    anatomic barriers •    physiologic barriers •    lysozyme •    phagocytosis •    endocytosis

•    inflammatory response •    antigenic specificity •    self/nonself recognition •    lymphocytes •    antigen presenting cells •    clonal selection •    antigen

P Key Concepts

n  Cells live in an internal environment that is actively maintained in a steady state. The immune response plays a central role in that maintenance. 

n  Disease is a shift in the steady state. Disease arises through infection by foreign agents, modification of healthy cells, transformation of cells, or failure of the normal regulatory function of cells, tissues or organs.

n  Protection against foreign agents is known as immunity. It may be innate and unchanging or it may be acquired. The protection may use circulating molecules such are antibodies or specific cell types or usually a combination of the two.

n  Immune responses are usually triggered by exposure to a specific foreign “non self” compound that is called an immunogen.  The immunogen evokes the production of specific antagonists which can either be antibodies that circulate in the body fluids or specific effector cells. (Pertussis)

DID YOU KNOW?

In “Did you know?” section we will use examples and anecdotes to clarify important ideas which are frequently misunderstood by many.  They are not found in your textbook however we strongly recommend reading this section because it reinforces the major concepts presented in the lessons.

The study of immunology as a science has gone through several periods of quiescence and active development, usually succeeding the introduction of a new technique or a changed paradigm of thinking about the subject.  We are currently in a phase of feverish activity, so productive that every textbook runs a considerable risk of being outdated before it appears in print.  For example factors such as nutrition, age and genetic makeup are well known to effect host defenses.  Recently scientists have noted that stress can also affect the efficacy of host immunity.  The basis for this is still speculative.  The emerging connections between the immune system and the nervous system are one of many new and exciting discoveries which, we hope, will help you appreciate the complexity and beauty of the living body.

Of  All the Nerve!  Emerging Connections Between the Immune System and the Nervous System

It has long been noted that stress or abuse of certain drugs (e.g., heroin, cocaine) are associated with decreased immune function, but the basis for this connection was not understood.  Some recent findings that suggest linkages between the nervous system and the immune system may ultimately provide an explanation of this connection.  Many of the body’s responses to environmental stress involve release of glucocorticoid hormones.  This class of compounds is known to be immunosuppressive when they are used therapeutically as anti-inflammatory agents, and abnormally high levels produced in response to stress within the body could have similar effects.  Another connection between the immune system and the nervous system is that sympathetic neurons are connected to the lymph system, which mediates antibody production.  In fact, there are receptors for catecholamine (a neuroactive compound) on the surface of the lymphoid tissue.  Catecholamines have been shown to suppress T cell activity in animals. Mast cells associated with the gastrointestinal tract release histamine and other compounds that can activate neurons in response to certain types of infections.  Finally, morphine, a compound that acts on the nervous system, is immunosuppressive, at least in mice.  These intriguing bits of information may be indications that an extensive interconnection exists between the nervous system and the immune system.

As appeared in: Bacterial Pathogenesis a Molecular Approach.  A. A. Salyers and D. D. Whitt.  ASM Press. Washington, DC. 1994

 

Immunization refers to various processes that promote increased immunity against specific disease.  With active immunization, an antigen-containing preparation known as a vaccine is either taken orally or injected into the body.  Passive immunization helps individuals already infected with pathogens to receive injections of purified antibody.  Here we present a routine immunization schedule as it is recommended by Ministry of Health in Ontario.

 

	2 mo.	4 mo.	6 mo.	12 mo*	18 mo.	4-6 yr.	14-16 yr.	Every 10 yr ** thereafter
Diphtheria	U	U	U		U	U	U	U
Pertussis	U	U	U		U	U
Tetanus	U	U	U!		U	U	U	U
Polio ***	U	U	U		U	U	U
Hib	U	U	U		U
Measles				U		U
Mumps				U		U
Rubella				U		U

*Must be after 1^st birthday.   **Td recommended.

*** If oral polio is given throughout, recommended schedule for OPV=2,4,18 months and 4-6 years.

Self Evaluation

Here we include a list of “acid tests” and “Do’s and Don’t’s” which we propose that you use for self evaluation when completing the review.  Included are recommendations for approaching the performance objectives as well as answering study questions such as definitions, short answers and diagrams.  Simply giving you the sample answer for each review question included here is not going to help you think about your answers.  In fact it may be very limiting since you will mistakenly assume that the given answer is the on ly way to approach the problem.  Once you follow these simple rules you should be able to answer your questions correctly.

Definitions:

1.  Do not use the term to define the term.  For example answer: antibody is an antibody... is not acceptable. The correct answer should be: antibody is a glycoprotein produced and secreted by B-cells.

2.  Do not use point form.  When you use point form we have to assume the connections between ideas listed as points.  We recommend using full sentences. In this way you are the one who includes the connections and we don’t have to assume anything.

3.  Do include appropriate examples.  As with any definition taken from the dictionary, examples should follow the definition.  For example:  Cytokine is a protein that mediates cellular interactions and regulates cell growth and secretion.  As a result, cytokines regulate the immune response.  Interleukins and Tumor Necrosis Factor are examples of cytokines.

How to Respond to a Short Answer Question

1.  Answer in the space provided.  One paragraph is sufficient. The questions on the exam will be very similar to the exercise questions, and the space for the answer will be limited too, so write your answers with this in mind.

2.  Build your answer by developing an introduction, followed by the main information and then close it with a brief summary. Organize the answer so it is clear, understandable and has a logical flow of ideas.  Think before you start writing!

3.  Do include the relevant information only.   Usually it is useful to ask yourself the following questions:   Do I gain anything by including that information?  Do I loose anything by not including that information? If the answer to both those questions is YES, then include it!  In addition answer the following questions:  Is the fact correct?  Is the fact related?  For example, when the question asks about the structure of IgM, and if your answer includes detailed information on function and biological characteristics of IgM it is not correct, even if the information is technically right, it is not the answer to the question.

4.  Relate facts in your answer.  Don’t assume that we will make connections for you.  For example when you are asked about function of lymphocytes, don’t expect us to make assumption that it is a cell. 

5.  Make sure that you answer in the correct format.  Depending on the question you may have to write a paragraph, construct a table, draw a diagram or create a list.  Pay attention to the organization of your answer; diagrams must be clearly labeled with directions and dynamics of the  processes indicated by arrows for example.

Review Questions

1. Textbook Study Questions

Review questions at the end of the Chapter 1.  The answers with explanations are available at the end of the textbook.

2.  Multiple Choice Questions (Answers can be found in the separate Answer Key.)

1.  Which of the following apply to “innate” immune mechanisms: