Immunity and Neutrophils- Types and Function

Last updated: February 8, 2026Reviewed date: February 8, 2026Reading time: 5 min read
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Immunity/The immune system is a host defense system comprising many biological structures and processes within an organism that protects against disease. To function properly, an immune system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms, and distinguish them from the organism's own healthy tissue. In many species, there are two major...

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বাংলা রোগী নোট এখনো যোগ করা হয়নি। পোস্ট এডিটরে “RX Bangla Patient Mode” বক্স থেকে সহজ বাংলা সারাংশ যোগ করুন।

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Article Summary

Immunity/The immune system is a host defense system comprising many biological structures and processes within an organism that protects against disease. To function properly, an immune system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms, and distinguish them from the organism's own healthy tissue. In many species, there are two major subsystems of the immune system: the innate immune system and the adaptive immune system. Both subsystems use humoral immunity and cell-mediated immunity to perform their functions. In...

Key Takeaways

  • This article explains Types of Immunity in simple medical language.
Educational health guideWritten for patient understanding and clinical awareness.
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Emergency safety firstUrgent warning signs are highlighted below.

Seek urgent medical care if you notice

These warning signs are general safety guidance. Local emergency numbers and clinical judgment should always come first.

  • Fever with very low white blood cells or known immune suppression.
  • Unusual bruising, persistent bleeding, black stools, or severe weakness.
  • Shortness of breath, fainting, confusion, or rapidly worsening fatigue.
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Use emergency care for severe, sudden, rapidly worsening, or life-threatening symptoms.

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Immunity/The immune system is a host defense system comprising many biological structures and processes within an organism that protects against disease. To function properly, an immune system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms, and distinguish them from the organism’s own healthy tissue. In many species, there are two major subsystems of the immune system: the innate immune system and the adaptive immune system. Both subsystems use humoral immunity and cell-mediated immunity to perform their functions. In humans, the blood–brain barrier, blood-cerebrospinal fluid barrier, and similar fluid–brain barriers separate the peripheral immune system from the neuroimmune system, which protects the brain.

Types of Immunity

Innate immunity – evolutionarily conserved rapid defense without immunologic memory

    • predominant cell types
      • phagocytes
        • neutrophils (polymorphonuclear leukocytes) are most abundant cells of innate immune system and earliest responders to infection
        • monocytes and macrophages are predominant immune cells at site of infection, or irritation, often causing pain, swelling, heat, or redness. সহজ বাংলা: শরীরের প্রদাহ; ব্যথা, ফোলা বা লালভাব হতে পারে।" data-rx-term="inflammation" data-rx-definition="Inflammation is the body’s response to injury, infection, or irritation, often causing pain, swelling, heat, or redness. সহজ বাংলা: শরীরের প্রদাহ; ব্যথা, ফোলা বা লালভাব হতে পারে।">inflammation several days after infection
      • natural killer (NK) cells kill infected, malignant, and stressed cells
      • mast cells are commonly found in mucosal tissues and are first responders to environmental antigens
      • dendritic cells are efficient in uptake and presentation of antigens for initiation of adaptive response
    • functions of innate immunity include
      • recognizing microbial components via pattern recognition receptors and initiating inflammatory response
      • removing and destroying pathogen-associated antigens through phagocytosis and complement activation
      • killing infected or stressed cells by NK cell-mediated cytotoxicity
      • transporting antigens to lymphoid tissues for adaptive response
    • Reference – Rich RR, Fleisher TA, Shearer WT, Schroeder H, Frew AJ, Weyand CM. Clinical Immunology. 5th ed. Elsevier; 2019
  • acquired or adaptive immunity – antigen-specific lymphocyte response that generates long-lasting immunological memory composed of 2 arms
    • humoral immunity – antibody (immunoglobulin)-producing B-cell response
    • cell-mediated (or cellular) immunity – major histocompatibility complex (MHC)-restricted T-cell response
    • Reference – Rich RR, Fleisher TA, Shearer WT, Schroeder H, Frew AJ, Weyand CM. Clinical Immunology. 5th ed. Elsevier; 2019
  • immunodeficiency
    • primary (congenital) immunodeficiency – genetic disorders leading to defects in development or function of the immune system
    • secondary (acquired) immunodeficiency – exposure to factors resulting in suppression of normal immune system, such as
      • malnutrition
      • HIV infection
      • immunosuppressive medications
      • malignancy
Neutrophils are a type of phagocyte and a major contributor to innate immune defense against bacteria and fungi1
  • Development
      • neutrophils arise from hematopoietic stem cells in bone marrow and cytoplasmic granules within neutrophils evolve throughout bacterial infection. সহজ বাংলা: ব্যাকটেরিয়ার বিরুদ্ধে লড়াই করা শ্বেত রক্তকণিকা।" data-rx-term="neutrophil" data-rx-definition="Neutrophil is a white blood cell important for fighting bacterial infection. সহজ বাংলা: ব্যাকটেরিয়ার বিরুদ্ধে লড়াই করা শ্বেত রক্তকণিকা।">neutrophil development
      • band (or stab) cells are immature neutrophils released into circulation
      • mature neutrophils are terminally differentiated cells incapable of further cell division
  • Neutrophils may be found in bone marrow, peripheral blood, adherent to endothelium, and in tissues
      • unique morphology with multilobed nucleus (polymorphonuclear) and numerous granules allows easy identification by light microscopy
      • express CD13, CD15, CD16 (Fc gamma receptor III), and CD89 (Fc alpha receptor) detectable via flow cytometry
      • about 3-6 × 109 cells/L may be found in peripheral blood, representing 30%-50% of circulating leukocytes
      • short half-life in circulation (about 7 hours), but can survive up to 2 days in tissues
  • bacterial infection. সহজ বাংলা: ব্যাকটেরিয়ার বিরুদ্ধে লড়াই করা শ্বেত রক্তকণিকা।" data-rx-term="neutrophil" data-rx-definition="Neutrophil is a white blood cell important for fighting bacterial infection. সহজ বাংলা: ব্যাকটেরিয়ার বিরুদ্ধে লড়াই করা শ্বেত রক্তকণিকা।">Neutrophil granules
  • Characteristics of bacterial infection. সহজ বাংলা: ব্যাকটেরিয়ার বিরুদ্ধে লড়াই করা শ্বেত রক্তকণিকা।" data-rx-term="neutrophil" data-rx-definition="Neutrophil is a white blood cell important for fighting bacterial infection. সহজ বাংলা: ব্যাকটেরিয়ার বিরুদ্ধে লড়াই করা শ্বেত রক্তকণিকা।">Neutrophil Granules
    • bacterial infection. সহজ বাংলা: ব্যাকটেরিয়ার বিরুদ্ধে লড়াই করা শ্বেত রক্তকণিকা।" data-rx-term="neutrophil" data-rx-definition="Neutrophil is a white blood cell important for fighting bacterial infection. সহজ বাংলা: ব্যাকটেরিয়ার বিরুদ্ধে লড়াই করা শ্বেত রক্তকণিকা।">neutrophil response
      • recruitment to tissues
        • proinflammatory cytokines such as tumor necrosis factor (TNF) and interleukin 1 (IL-1) beta as well as chemokines recruit neutrophils to sites of infection
        • activation by cytokines and chemokines results in translocation of adhesion molecules to cell surface and allows rolling of neutrophils along endothelium
        • integrins on neutrophils bind intracellular adhesion molecules (ICAMs) on endothelium to adhere
        • after adhesion, neutrophils transmigrate between endothelial cells into extracellular matrix of tissue
      • microbial killing facilitated by
        • release of proteases, acid hydrolases, and inflammatory mediators within granules (degranulation) into extracellular fluid
        • phagocytosis of microbes and fusion of phagosomes with granules to form phagolysosomes that digest phagosome contents
        • production of reactive oxygen species with antimicrobial activity by phagocyte-derived nicotinamide adenine dinucleotide phosphate (NADPH) oxidase
        • release of bacterial infection. সহজ বাংলা: ব্যাকটেরিয়ার বিরুদ্ধে লড়াই করা শ্বেত রক্তকণিকা।" data-rx-term="neutrophil" data-rx-definition="Neutrophil is a white blood cell important for fighting bacterial infection. সহজ বাংলা: ব্যাকটেরিয়ার বিরুদ্ধে লড়াই করা শ্বেত রক্তকণিকা।">neutrophil extracellular traps (NETs) to capture microbes and digest them via autophagy
  • evaluation of infection. সহজ বাংলা: ব্যাকটেরিয়ার বিরুদ্ধে লড়াই করা শ্বেত রক্তকণিকা।" data-rx-term="neutrophil" data-rx-definition="Neutrophil is a white blood cell important for fighting bacterial infection. সহজ বাংলা: ব্যাকটেরিয়ার বিরুদ্ধে লড়াই করা শ্বেত রক্তকণিকা।">neutrophil counts by complete blood count (CBC) and blood smear
    • absolute neutrophil count (ANC) includes segmented neutrophils (also called polymorphonuclear cells) and band forms
      • neutropenia defined as ANC ≤ 1.5 × 109/L
      • neutrophilia defined as ANC > 7-7.7 × 109/L
    • band neutrophils
      • immature neutrophils
      • morphologically characterized by absence of complete separation of nuclear lobes with a visible distinction between chromatin and parachromatin in the narrowest segment of the nucleus
      • often flagged on 5-part automated differential and confirmed by manual inspection of peripheral blood smear
    • immature/total granulocyte (I/T-G) ratio
      • defined as immature neutrophil count (myelocytes + metamyelocytes + bands +/- promyelocytes)/total neutrophil count
      • used as an indicator of a granulocyte left shift
    • granulocyte left shift indicates an abnormally high proportion of immature neutrophils in the blood, defined as either
      • increased band neutrophils in the peripheral blood (typically > 10% of WBC) by manual differential cell count
      • elevated I/T-G ratio by manual differential cell count
      • elevated number or percent of immature granulocytes detected by automated cell analyzer, which typically represents promyelocytes, myelocytes, and metamyelocytes (but not blasts)

Classifications of Primary Immunodeficiency Disorders

Disorders of neutrophils are typically classified as congenital defects of phagocyte number, function, or both classification of primary immunodeficiency disorders as stated by the American Academy of Allergy, Asthma, & Immunology (AAAAI), American College of Allergy, Asthma, & Immunology (ACAAI), and Joint Council of Allergy, Asthma and Immunology (JCAAI)

  • combined B- and T-cell immunodeficiencies
  • well-defined syndromes with immunodeficiency
  • predominantly antibody deficiencies
  • diseases of immune dysregulation
  • congenital defects of phagocyte number, function, or both
  • defects of innate immunity
  • autoinflammatory disorders
  • complement deficiencies

Classification of primary immunodeficiency disorders as stated by the Primary Immunodeficiency Expert Committee (PID EC) of the International Union of Immunological Societies (IUIS)

  • immunodeficiencies affecting cellular and humoral immunity
  • combined immunodeficiencies with associated or syndromic features
  • predominantly antibody deficiencies
  • diseases of immune dysregulation
  • congenital defects of phagocyte number or function
  • defects in intrinsic and innate immunity
  • autoinflammatory disorders
  • complement deficiencies

References

 

 

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Doctor to discuss: Doctor / qualified healthcare provider
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  • Relevant blood, urine, imaging, or specialist tests only after clinical assessment
Questions to ask
  • What is the most likely cause of my symptoms?
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Care roadmap for: Immunity and Neutrophils- Types and Function

Use this simple roadmap to understand the next safe steps. It is educational and does not replace examination by a doctor.

Go to emergency care if you notice:
  • Severe or rapidly worsening symptoms
  • Breathing difficulty, chest pain, fainting, confusion, severe weakness, major injury, or severe dehydration
Doctor / service to discuss: Qualified healthcare provider; specialist depends on symptoms and examination.
  1. Step 1

    Check danger signs first

    If danger signs are present, seek emergency care and do not wait for online information.

  2. Step 2

    Record the symptom story

    Write when symptoms started, severity, medicines already taken, allergies, pregnancy status, and test results.

  3. Step 3

    Visit a qualified clinician

    A doctor, nurse, or qualified healthcare provider can examine you and decide which tests or treatment are needed.

  4. Step 4

    Do only useful tests

    Do tests after clinical assessment. Avoid unnecessary tests, random antibiotics, or repeated medicines without diagnosis.

  5. Step 5

    Follow up and return early if worse

    If symptoms worsen, new warning signs appear, or treatment is not helping, return for review quickly.

Rural patient practical tips
  • Take a written symptom diary and all previous prescriptions/test reports.
  • Do not hide medicines already taken, even herbal or over-the-counter medicines.
  • Ask which warning signs mean urgent referral to hospital.

This roadmap is for education. A real diagnosis and treatment plan requires history, examination, and clinical judgment.

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Frequently Asked Questions

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