For the reasons outlined above it is important that when blood transfusions take place blood types are cross-matched beforehand. This is done by typing the patient’s blood by mixing a sample of it with various anti-sera to screen for antibodies and checking for agglutination. At room temperature agglutination, and not haemolysis, is visible to the naked eye indicating incompatibility. It is then cross-matched against the potential donor’s blood by checking that the plasma of the recipient does not contain any antibodies which would react against the donor erythrocytes. If none are present the transfusion can go ahead.
The absence of any anti-A or anti-B antibodies in the blood type AB means that blood from any of the four types can be used in transfusions for individuals of this blood type as they have no antibodies which could potentially react with antigens on red blood cells of the donor blood. For this reason the AB blood group can be referred to as the universal recipient. As there are no antigens on the O type red blood cell this type is also known as the universal donor meaning that blood from this type can be donated to individuals from all four blood types – there would be no reaction from any antibodies present in the recipient’s blood. The terms universal donor and universal recipient are not strictly correct however as blood can contain both antigens and antibodies from other systems other than that which is under consideration. The rhesus group is of importance here . . .
METHOD
As per the schedule and instructions given during the practical.
N.B. The slides were not checked under the microscope, as the reactions were visible to the naked eye as stated in the introduction.
RESULTS
Table 1
Table 2
Key
+ indicates agglutination.
X indicates no reaction.
DISCUSSION
From the results the following can be deduced :
Sample P1 is blood type A as it reacts with anti-A serum and anti-A & B serum. The antigen A present in the sample would react with the anti-A antibodies present in both sera.
Sample P2 is blood type B as it reacts with anti-B serum and anti-A & B serum. The antigen B present in the sample would react with the anti-B antibodies present in both sera.
Sample P3 is blood type AB as it reacts with anti-A, anti-B and anti-A & B sera. Antigens A and B present in the sample would react with the anti-A antibodies in the first serum, the anti-B antibodies present the second serum and both present in the third serum.
Sample P4 is blood type O as it reacts with none of the sera. Having no antigens present no reactions occur.
The lack of any reaction of any of the samples with the AB serum is for the following reason. There are no antibodies present in this serum and so no reaction occurs with the antigens of the samples.
THE MORPHOLOGY OF LEUCOCYTES
Leucocytes, or white blood cells (WBCs), represent along with platelets about 1% of the formed elements of blood. Their overall function is as a part of the immune response and each type of WBC is specialised to defend against particular invaders by different means and secretions. There are five types which shall be detailed in order of their abundance in the body.
1. NEUTROPHILS or POLYMORPHONUCLEOCYTES (PMNs)
These are categorised as granulocytes and constitute 60 -70 % of the total number of WBCs. The granules are small and evenly distributed and stain pale lilac. Contained within the granules are various types of chemicals which are activated to destroy invaders once the cell has phagocytised these foreign bodies. Amongst these chemicals are :
- lysozyme – an enzyme which kills bacteria
- superoxide anion, hydrogen peroxide and hypochlorite anion – strong antioxidants
- defensins – types of proteins which act as antibiotics and anti-fungal agents.
The term PMN refers to the multi-lobed nature of the nucleus – it can have from two to five lobes which are connected by strands of chromatin. Neutrophils are the first line defenders against infection and an increase in number indicates a bacterial infection.
2. LYMPHOCYTES
These are termed agranular as although they do possess granules they are small stain poorly and are not visible under the light microscope. They constitute 20 – 25 % of all WBCs. Also known as immunocytes they differentiate into three types – B cells, T cells and natural killer cells. All originate in the bone marrow but T cells undergo modification in the thymus. They are non-phagocytic and instead perform their functions through the production of antibodies and memory cells. These last contribute to long – lasting immunity.
3. MONOCYTES
These represent 3 – 8 % of all WBCs. Termed agranular they do in fact contain granules but as with lymphocytes they are small and stain poorly, however are important as these cells are phagocytic and require the chemicals contained within the granules to destroy invaders. Upon arrival at a site of infection they enlarge to become macrophages which have a limited capacity of matter ingested.
4. EOSINOPHILS
These are granulocytes which contain large granules that stain red/orange in an acidic dye. They constitute 2 – 4 % of all WBCs. Their role is in combating allergic reactions releasing enzymes such as histaminase and they also act as phagocytes against parasites.
5. BASOPHILS
Containing large granules which stain deep purple/blue in basic dyes these granulocytes comprise 0.5 – 1 % of all WBCs. Their function is in the secretion of histamine – important in the allergic response, and heparin which acts to prevent blood clotting and helps in the removal of fats from the bloodstream after a fat-rich meal.
BIBIOGRAPHY
.Fox, S. I. (1991). Human Physiology, 6th Edition. USA : Mcgraw/Hill.
Hoffbrand A. V. & Pettit J. E., (1993). Essential Haematology. Blackwell Science
