Blood Groups, Rh Factor, Transfusion Rules, and Immunity — Complete Biology Notes

Blood groups and immunity are high-frequency topics in Kerala PSC exams. This note covers the ABO system, Rh factor, transfusion rules, types of immunity, and the Indian vaccination schedule.

ABO Blood Group System

Discovered by Karl Landsteiner in 1900 (Nobel Prize in Physiology/Medicine, 1930).

Antigens and Antibodies

Blood Group	Antigen on RBC	Antibody in Plasma	Genotype
A	A	Anti-B	IA IA or IA i
B	B	Anti-A	IB IB or IB i
AB	A and B	None	IA IB
O	None	Anti-A and Anti-B	ii

Key Points:

• Antigens are proteins on the surface of red blood cells
• Antibodies are proteins in the plasma that attack foreign antigens
• Blood group is determined by co-dominant alleles (IA and IB are co-dominant; i is recessive)

Blood Group Inheritance

Parent 1	Parent 2	Possible Children
A x A	—	A or O
A x B	—	A, B, AB, or O
A x AB	—	A, B, or AB
A x O	—	A or O
B x B	—	B or O
B x AB	—	A, B, or AB
B x O	—	B or O
AB x AB	—	A, B, or AB (never O)
AB x O	—	A or B (never AB or O)
O x O	—	O only

Rh Factor

Discovered by Landsteiner and Wiener in 1940 using Rhesus monkey blood.

Rh Type	Antigen	Frequency in India
Rh+ (Positive)	Rh antigen (D antigen) present	~95% of Indians
Rh- (Negative)	Rh antigen absent	~5% of Indians

Erythroblastosis Fetalis (Rh Incompatibility)

Aspect	Detail
Occurs when	Rh-negative mother carries Rh-positive foetus (second pregnancy)
Mechanism	Mother develops anti-Rh antibodies after first pregnancy; these cross placenta in subsequent pregnancy
Effect	Destruction of foetal RBCs (haemolytic disease of newborn)
Prevention	RhoGAM injection (anti-D immunoglobulin) given to Rh- mother within 72 hours of first delivery

Blood Transfusion Compatibility

Who Can Donate to Whom?

Donor Group	Can Donate To
O-	All groups (Universal Donor)
O+	O+, A+, B+, AB+
A-	A-, A+, AB-, AB+
A+	A+, AB+
B-	B-, B+, AB-, AB+
B+	B+, AB+
AB-	AB-, AB+
AB+	AB+ only

Who Can Receive from Whom?

Recipient Group	Can Receive From
AB+	All groups (Universal Recipient)
AB-	AB-, A-, B-, O-
A+	A+, A-, O+, O-
A-	A-, O-
B+	B+, B-, O+, O-
B-	B-, O-
O+	O+, O-
O-	O- only

Key Terms

Term	Meaning
Universal Donor	O- (no antigens, no Rh)
Universal Recipient	AB+ (no antibodies, has Rh)
Agglutination	Clumping of RBCs when incompatible blood is mixed
Cross-matching	Testing donor and recipient blood for compatibility before transfusion

Blood Components and Facts

Component	Detail
RBC (Erythrocytes)	Carry oxygen; no nucleus in mature RBCs; life span ~120 days
WBC (Leucocytes)	Immunity; has nucleus; life span varies (hours to years)
Platelets (Thrombocytes)	Blood clotting; life span ~5-9 days
Plasma	55% of blood; contains water, proteins, antibodies
Blood volume in adult	~5-6 litres
pH of blood	7.35-7.45 (slightly alkaline)
Blood bank storage	RBCs stored at 4 deg C for up to 42 days
Platelets storage	20-24 deg C with agitation, 5 days

Types of Immunity

Classification

Type	Subtype	How Acquired	Duration	Example
Innate (Non-specific)	—	Born with it	Lifelong	Skin, mucous membranes, stomach acid, phagocytes
Acquired (Adaptive/Specific)	Active — Natural	Body fights infection	Long-lasting	Recovering from chickenpox
Acquired	Active — Artificial	Vaccination	Long-lasting	Polio vaccine, COVID vaccine
Acquired	Passive — Natural	Mother to child	Temporary (months)	Antibodies via placenta or breast milk (colostrum)
Acquired	Passive — Artificial	Pre-formed antibodies injected	Temporary (weeks)	Anti-tetanus serum, anti-venom

Active vs Passive Immunity

Feature	Active Immunity	Passive Immunity
Antibodies produced by	Own body	Received from outside
Time to develop	Slow (days to weeks)	Immediate
Duration	Long-lasting (memory cells)	Short-lived (weeks to months)
Memory cells	Formed	Not formed
Example	Vaccination, natural infection	Maternal antibodies, anti-serum

Antigens and Antibodies

Feature	Antigen	Antibody (Immunoglobulin)
Nature	Foreign substance that triggers immune response	Protein produced by B-lymphocytes
Also called	Immunogen	Immunoglobulin (Ig)
Types of Ig	—	IgG, IgA, IgM, IgE, IgD

Types of Immunoglobulins

Ig Type	Key Feature
IgG	Most abundant (75%); crosses placenta; secondary immune response
IgA	Found in secretions (saliva, tears, breast milk); mucosal immunity
IgM	Largest antibody; first to respond (primary immune response)
IgE	Allergic reactions; defence against parasites
IgD	Found on B-cell surface; least understood

Indian Vaccination Schedule (National Immunisation Schedule)

Age	Vaccine	Disease
At birth	BCG, OPV-0, Hepatitis B birth dose	TB, Polio, Hepatitis B
6 weeks	OPV-1, Pentavalent-1, Rotavirus-1, fIPV-1, PCV-1	Polio, DPT+HepB+Hib, Rotavirus, Polio (injectable), Pneumococcal
10 weeks	OPV-2, Pentavalent-2, Rotavirus-2	Same as above
14 weeks	OPV-3, Pentavalent-3, Rotavirus-3, fIPV-2, PCV-2	Same as above
9 months	MR-1 (Measles-Rubella), PCV booster	Measles, Rubella, Pneumococcal
16-24 months	MR-2, OPV booster, DPT booster-1	Measles, Polio, DPT
5-6 years	DPT booster-2	Diphtheria, Pertussis, Tetanus
10 years	TT (Tetanus Toxoid)	Tetanus
16 years	TT	Tetanus

Key Vaccine Facts

Vaccine	Type	Developer/Discovery
BCG	Live attenuated	Albert Calmette and Camille Guerin
OPV (Sabin)	Live attenuated (oral)	Albert Sabin
IPV (Salk)	Inactivated (injectable)	Jonas Salk
Smallpox vaccine	First vaccine ever	Edward Jenner (1796)
Rabies vaccine	Killed virus	Louis Pasteur

Frequently Asked PSC Questions

Q1. Who discovered blood groups? Ans: Karl Landsteiner (1900)

Q2. Which blood group is called the Universal Donor? Ans: O negative (O-)

Q3. Which blood group is the Universal Recipient? Ans: AB positive (AB+)

Q4. What causes erythroblastosis fetalis? Ans: Rh incompatibility between Rh-negative mother and Rh-positive foetus

Q5. Which antibody crosses the placenta? Ans: IgG

Q6. Which is the largest antibody? Ans: IgM

Q7. Who developed the first vaccine? Ans: Edward Jenner (smallpox vaccine, 1796)

Q8. Colostrum provides which type of immunity to the newborn? Ans: Passive natural immunity

Q9. What is the life span of RBCs? Ans: Approximately 120 days

Q10. Which immunoglobulin is involved in allergic reactions? Ans: IgE