ABO/Rh Blood-Typing Model:

o … what’s happening here?” is a ques-tion commonly heard when introductory science students are working on cellular or molecu-lar laboratory concepts. Since there is a huge variety in student expectations, abilities, and needs in any introductory science course, consideration must be made for the diverse ways students learn. Pictures and visual demonstrations certainly help, but three-dimensional manipulative models literally put those cells and molecules into the students’ hands. Then they can not only see, but also manipulate and phys-ically process the major principles being addressed. A prime example of this difficulty for many stu-dents is the cellular/molecular nature of blood typ-ing. For this reason, I was interested in developing an effective, inexpensive way of illustrating the processes taking place in students’ blood-typing trays during this lab exercise. The ABO/Rh

Blood-Typing Model kit described here has been effective-ly used by university students in both my majors’ and non-majors’ biology labs:

• to solve problems related to normal blood-typing activities

• to investigate how mismatched blood types can result in transfusion reactions

• to understand how parental blood types may cause erythroblastosis fetalis in the fetus • to identify and correct student

misconcep-tions about antibody/antigen interacmisconcep-tions and normal antibody production

• to practice their problem-solving skills, rather than simply memorizing isolated facts, through manipulation of the model cells.

Description of the Model

The model consists of a biconcave StyrofoamTM red blood cell (RBC) with a three-dimensional aspect that provides a better understanding of the

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ABO/Rh Blood-Typing Model:

A Problem-Solving Activity

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CAROLM. F. WAKE, Ph.D. is Associate Professor of Biology at

South Dakota State University, Brookings, SD 57007; e-mail: [email protected].

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microscopic images that students study in lab. The RBC model accommodates several pushpin surface-marking antigens. To reinforce the surface-marker specificity concept, pushpin antigens are appropriately labeled and color-coordinated with matching chenille-stem antibodies. The design of anti-A, B, and Rh antibody models denotes the antigen-binding sites of the vari-able regions at the arms of the Y-shaped molecule. The antibody models may be used to represent naturally occurring antibodies found in blood sera or they may be labeled and used to demonstrate the artificial anti-bodies present in simulated blood-typing kits used in students’ lab activities. A complete list of materials and a description of model construction is presented in Table 1 and illustrated in Figures 1-3. A complete ABO/Rh Blood-Typing Model, as depicted, can be assembled for two to three dollars. We package the

model kits in plastic bags, together with an Application Sheet (see Web address in conclusion) for use by pairs of students in lab class. Students may also check out model kits from their instructors for review at home. These materials are used to demonstrate basic blood-typing, transfusion reac-tions, and Rh incompatibility.

University Student-Lab

Applications

In my university introductory biol-ogy classes, the ABO/Rh Blood-Typing Model kit is a component of a lab exercise on blood-typing that also includes examination of prepared slides of human and avian blood smears and analysis of blood types using simulated blood-typing kits. For maximum efficacy, each pair of students is provided with a model kit and an Application Sheet (see Web address in conclusion). We begin the lab period with a general review of the molecular structures, location, and production of A, B, and Rh antigens and antibodies. The antibody model shape represents the “cleft” at the ends of the variable regions (short arms) of the Y-shaped antibody and pro-vides an analogy for the binding-site specificity between antibodies and antigens. As they are working through the rest of their lab activities, student teams are asked to demonstrate solutions to the following problem-solving activity sets.

Figure 1.

ABO/Rh Blood-Typing kit. A. Materials to construct one kit, as listed in Table 1. B. Completed ABO/Rh Blood-Typing kit. For the Application Sheet, see the Web address listed in the Conclusions section.

A.

B.

Table 1. Materials needed to construct one ABO/Rh Blood-Typing kit.

RBCs Two Styrofoam™ balls (2 1/2”), red water-based paint, varnish Antigens Yellow, blue, and green pushpins (three each)

Antibodies Yellow, blue, and green chenille-stems (14” long, two each) Yellow, blue, and green self adhesive page-markers (four each) Kit completion Glue, black permanent marker, small self-closing plastic bag Application Sheet Clear page protector, printed Application Sheet

Activity Set 1: Blood Typing

Construct each of the four different ABO blood types, with all possible combinations of Rh factor. Check your work for accuracy with your instructor before proceeding and then answer the questions below.

When looking at RBCs with the microscope, why do they appear lighter-colored in the mid-dle? (The biconcave structure)

Where are antigens located? (Protein molecules

extending from the surface of the RBC membrane)

Are antigens visible with the microscope? (No,

molecules are too small)

Antibodies are composed of what type of organ-ic molecule? (Proteins-amino acid sequences make

up two short and two long polypeptides, the light and heavy chains, respectively)

Where in the body are antibodies made?

(Lymphocyte B-cells)

Activity Set 2: Transfusion Reactions

Construct transfusion scenarios for different blood types. By arranging and rearranging antigen markers on the cells, demonstrate to your instructor agglutination reactions or compatible transfusions. Remember that, unlike recipients’ blood, donor blood samples include only blood cells with their resident surface-marking

Figure 3.

Construction of Antigens/Antibodies. A. Label pushpin antigens with a black permanent marker. B. Cut chenille-stems in half, fold them in half again, and insert and glue a matching page-marker into place.Twist the chenille-stem into the “Y” antibody shape, making binding-site hooks at the “variable region” ends of the molecule. C. Make simulated anti-A, B, and Rh antibodies and label by gluing additional page-markers into place.

A.

B.

C.

Figure 2.

Construction of RBC. A. Using your hand or other flat surface, slowly press the Styrofoam™ ball flat. Quick pressure will cause the ball to break rather than flatten. B. Using a billiard ball or other small hard sphere, indent both flat surfaces to make the biconcave shape. C. Apply several light coats of latex red spray paint.

antigens but not the serum containing any antibodies. Which blood type is the universal donor? Why?

(O, no A or B antigens on the surface of the donat-ed RBC)

Which is the universal recipient? Why? (AB, no

anti-A or B antibody in the blood serum to react with either antigen)

Activity Set 3: Rh Incompatibility

Reactions

Construct a scenario with an Rh-negative mother, pregnant with either an Rh-negative or Rh-positive fetus. Demonstrate your understanding of the process and consequences of Rh incompatibility between mother and fetus by answering the following questions.

Does an Rh-negative person have Rh bodies? Why?/Why not? (No, unlike A or B

anti-gens, Rh antigens are not ubiquitous)

In what organism were Rh antigens first found (and thus received the name)? (Rhesus monkey) When can the mother’s blood become sensi-tized to Rh antigens? (During labor/delivery of

an Rh-positive baby)

Why is Rh incompatibility a problem, while A or B incompatibilities are not? (Rh antibodies are

smaller so that they are able to pass through the placental membrane. There are, however, rare occurrences of A or B incompatibilities, too.)

Identification of Conceptual

Problems

We check students’ initial model setups for accuracy before they proceed with the exercise. Many of the students’ misconcep-tions about blood cells, antigens, and antibodies can be identified and corrected right away. The following are some specific concept struggles you might anticipate and how they might be resolved.

• To understand the difference between naturally-occurring antibodies in a blood sample and simulated anti-A, B, or Rh antibodies that are reagents in the simulated blood-typing kit.

(Through the use of labeled sim-ulated A, B, and Rh anti-body models, students are able

to distinguish between blood-typing reagents and naturally occurring antibodies. Most students under-stand the binding of matching antigens and antibod-ies, but a visual representation of the simulated anti-A, B, or Rh antibody reagent is a vivid reminder of the agglutination concept.)

• To distinguish between what constitutes a donor’s blood sample and the recipient’s blood.

(When students “construct” both the donor’s contri-bution [packed RBCs] and the recipient’s blood [RBCs and serum with constituent antibodies], the concepts of universal donor/universal recipient become very simple.)

• To realize the ubiquitous nature of A and B anti-gens (but not Rh) in our environment and the subsequent antibody-production immune response. During this problem identification activity, we frequently see representations of Rh-negative blood samples that incorrectly contain anti-Rh antibodies.

(This problem is very quickly identified and correct-ed as students practice constructing models of differ-ent blood types.)

• To remember the difference between the words “antigen” and “antibody”.

(Antibody ends with the letter “Y”, which is reminis-cent of its shape.)

For effective learning to take place, it is very impor-tant to avoid, or very quickly correct, misconceptions. Through the utilization of these hands-on materials, stu-dents and instructors are able to interactively participate in this process.

Conclusions

The ABO/Rh Blood-Typing Model kits have been used for the past several years by thousands of students in our introductory biology classes. Hundreds of model kits have been distributed to area high school science teachers for their use and information. A Spanish ver-sion of the Application Sheet has been developed and model kits are also being used at our sister university, Universidad Academica Campesina, Carmen Pampa, Bolivia. The Application Sheet can be found online (English or Spanish version) at my Web site (http:// biomicro.sdstate.edu/wakec/Rbcweb/index.htm). With a small grant, we have also fabricated a more resilient polypropylene version of the ABO/Rh Blood-Typing Model kit which is available from Ward’s Natural Science, Inc. (http://www.wardsci.com/product.asp? pn=148327).

Our university instructors have found that the model kits and Activity Sets facilitate visualization of the physical biconcave structure of red blood cells and con-ceptualization of blood-typing principles. The model kits also enable students to identify relationships between A, B, and Rh antigens/antibodies in blood and to understand molecular mechanisms involved in trans-fusion agglutination reactions. This model kit and activ-ities are easily adaptable to many levels of biology cours-es including: introductory biology and immunology at college and university levels, as well as technical school and advanced-placement high school and middle school science classes. Instructors are able to customize them for the particular academic emphasis and acumen of their students.

Through manipulation of the model cells, students practice their problem-solving skills, rather than simply memorizing isolated facts. “Effective teaching considers whether the student is learning by observing the stu-dents’ application of concepts …” (Krause, 1998).

Acknowledgments

I acknowledge South Dakota State University for The New Ideas Grant financial support and my col-leagues who helped “field” test early prototypes during development of this teaching model.

References

Krause L. (1998). The cognitive profile model of learning styles: differences in student achievement in general chemistry. Journal of College Science Teaching, 28 (September/October), 57.