Disorders of Lymphocytes

Characteristics of Lymphocytes

The normal range for lymphocytes in an adult is 22% to 40%, with absolute values of 1.1 to 4.4 × 10^9/L.
Absolute number is calculated as:
- Absolute number = total leukocyte count × relative % of lymphocytes.
A value less than the normal reference range is designated as lymphocytopenia.
When the blood lymphocyte count exceeds the upper limit of the normal reference range, the condition is termed lymphocytosis.

Lymphocytosis

Lymphocytosis is a condition that can be natural and normal in infants and children up to approximately 10 years old, with total lymphocyte counts possibly reaching 9 × 10^9/L.
- This increase is likely due to limited production of adrenal corticosteroid hormones during this developmental stage.
- Limited hormone production may also underlie lymphocytosis observed during later childhood in conditions such as malnutrition and scurvy.
Lymphocytosis is not a common nonspecific response to inflammation, unlike neutrophilia.

Non-malignant Conditions Associated with Lymphocytosis

In adolescence and adulthood, non-malignant conditions linked to absolute lymphocytosis include:
- Acute viral infections:
- Infectious mononucleosis
- Infectious hepatitis
- Posttransfusion syndrome
- Cytomegalovirus (CMV) infection
- Infectious lymphocytosis
- Specific bacterial infections:
- Bordetella pertussis (whooping cough)
- Brucellosis
- Parasitic infections, particularly toxoplasmosis.
- Drug reactions, including hypersensitivity to p-aminosalicylic acid and phenytoin.
- Uncommon causes such as tertiary and congenital syphilis and smallpox.

Malignant Conditions Producing Lymphocytosis

Malignant conditions that may produce lymphocytosis include:
- Lymphocytic leukemia (both acute and chronic forms)
- The leukemic phase of lymphomas
- Waldenström’s macroglobulinemia
- Various cancers.

Disorders Associated with Lymphocytosis

The following diseases are associated with lymphocytosis:
- Infectious mononucleosis
- Cytomegalovirus infection
- Toxoplasmosis
- Infectious lymphocytosis
- Bordetella pertussis infection.

Infectious Mononucleosis

Typically an acute, benign, and self-limiting lymphoproliferative condition caused by the Epstein-Barr virus (EBV).
EBV is also linked to other malignancies:
- Burkitt’s lymphoma, a malignant tumor of lymphoid tissue, primarily affecting African children.
- Nasopharyngeal carcinoma.
- Neoplasms of the thymus, parotid gland, and supraglottic larynx.

Etiology of Infectious Mononucleosis

EBV is the most ubiquitous virus known to humans, estimated that 95% of the global population is exposed to it.
Classified as a human herpes DNA virus.
The virus infects B lymphocytes; however, the variant lymphocytes that result from the infection exhibit T-cell characteristics upon microscopic examination of peripheral blood.

Epidemiology of EBV

EBV is typically transmitted through close contact with oropharyngeal secretions; it can also be transmitted via blood transfusions and transplacental routes.
The prevalence of seronegativity for EBV is nearly 100% in early infancy, decreasing to less than 10% in young adults.
After initial exposure, patients are generally immune and not susceptible to reinfections, though infections can be severe in immunocompromised patients.

Clinical Signs and Symptoms of Infectious Mononucleosis

Majority of individuals seroconvert without any signs or symptoms.
In individuals under age 5, infections are mostly asymptomatic or exhibit poorly defined signs and symptoms.
The incubation period lasts approximately 10 to 50 days, with symptoms persisting for 1 to 4 weeks.
Common clinical symptoms are:
- Extreme fatigue
- Malaise
- Sore throat
- Fever
- Cervical lymphadenopathy
Splenomegaly occurs in about 50% of patients.
The most common complication is viral hepatitis.

Laboratory Data for Infectious Mononucleosis

Laboratory testing is essential for the diagnosis.
Hematological studies indicate leukocyte counts from 10 to 20 × 10^9/L in approximately two-thirds of patients, while about 10% of patients exhibit leukopenia.
A differential leukocyte count may initially show neutrophilia, but mononuclear cells typically dominate as the disease progresses.
Normal lymphocyte counts range from 60% to 90%, with 5% to 30% being variant lymphocytes. These variant lymphocytes show diverse morphological features and can persist for 1 to 2 months in some patients or even 4 to 6 months in others.

Antibody Testing for Infectious Mononucleosis

Diagnosis may involve antibody testing for heterophil antibodies and EBV-specific antibodies.
Rapid slide tests utilize horse erythrocyte agglutination to enhance sensitivity, yet most heterophil tests lack specificity for infectious mononucleosis.

Summary of Antibody Profiles in Infectious Mononucleosis

Timeframe	VCA IgM	VCA IgG	EA-D	EA-R	EBNA IgG	Heterophil
No previous exposure	-	-	-	-	-	-
Recent infection	+	+	+	-	-	+
Past infection	-	+	-	+	+	+
Reactivation of latent infection	-	+	-	-	+	±

VCA represents viral capsid antigen, EA-D refers to early antigen (diffuse), EA-R for early antigen (restricted), while EBNA stands for Epstein-Barr nuclear antigen.

Cytomegalovirus Infection: Etiology

Cytomegalovirus (CMV) is classified within the herpes family of viruses—other members include herpes simplex I, herpes simplex II, varicella-zoster virus, and EBV.
Hematological examinations in CMV infection commonly reveal leukocytosis, often with slight lymphocytosis exceeding 20% variant lymphocytes.
Abnormal liver function may be noted in clinical chemistry tests.
The definitive diagnosis of CMV infection is established by isolating the virus from urine or blood samples or by detecting CMV-specific IgM or increasing CMV-specific IgG antibody titers.

Cytomegalovirus Infection: Epidemiology

CMV is a ubiquitous viral pathogen globally.
Requires intimate contact with secretions of infected individuals for transmission, including:
- Urine
- Respiratory secretions
- Tears
- Feces
- Genital secretions
- Blood and breast milk
Active CMV infection leads to considerable morbidity and mortality in AIDS patients and can present as a latent infection characterized by reactivation.

Clinical Signs and Symptoms of Cytomegalovirus Infection

Acquired CMV infection is often asymptomatic; may persist as a chronic or latent infection.
Occasionally, symptoms may mimic a self-limited, heterophil-negative mononucleosis-like syndrome, including:
- Sore throat
- Fever
- Chills
- Profound malaise
- Myalgia
- Lymphadenopathy and splenomegaly may also be present.
While symptoms are mild in healthy individuals, they can be life-threatening for immunocompromised patients.

Laboratory Data for Cytomegalovirus Infection

Characteristic leukocytosis with slight lymphocytosis (greater than 20% variant lymphocytes) is common.
Liver function tests typically show abnormalities.
Definitive diagnosis made by identifying the virus in blood/urine samples or detecting increasing CMV-specific IgG/IgM antibodies.

Toxoplasmosis

Etiology

Toxoplasmosis is caused by the organism Toxoplasma gondii, a newly recognized tissue Coccidia.
Clinical and laboratory findings resemble infectious mononucleosis, including an increased presence of variant lymphocytes on blood smear.
Diagnosis is confirmed serologically through the detection of significant elevations in Toxoplasma antibodies.

Epidemiology of Toxoplasmosis

Toxoplasma gondii infects both humans and animals, predominantly in rodents and various birds and mammals.
The definitive host is the house cat and other members of the Felidae family.
Humans may contract the infection through ingestion of oocysts shed in cat feces or contaminated food, water, or contact with inadequate meat or raw milk.

Transmission

Transplacental transmission occurs in all mammals, including humans, especially during acute but often unnoticed maternal infections.
Approximately 45% of untreated women who acquire an initial infection will give birth to congenitally infected infants.

Clinical Signs and Symptoms

Typically asymptomatic in adults and children; when symptoms occur, they are mild and often not detectable.
Symptoms can mirror infectious mononucleosis with:
- Chills
- Fever
- Headache
- Lymphadenopathy
- Extreme fatigue
In immunocompromised individuals, severity is heightened.
Congenital toxoplasmosis can lead to CNS malformations or prenatal mortality, impacting newborns who may remain dormant until symptoms emerge later on.

Laboratory Data for Toxoplasmosis

Similar to infectious mononucleosis.
Presence of variant lymphocytes on peripheral blood smear.
Diagnosis confirmed by significant increases in Toxoplasma gondii antibodies detectable within 2 weeks of infection; the organism cannot be cultured.

Infectious Lymphocytosis

Characterized by leukocytosis displaying lymphocytosis that may precede clinical symptoms, with leukocyte counts ranging from 20 to 50 × 10^9/L.
Differential counts can show up to 95% small, mature, normal lymphocytes, likely of T-cell origin. No lymphoblasts are found, though eosinophil levels may increase.
Heterophil and EBV antibody tests typically yield negative results.
In children with the chronic form, leukocyte counts often range from 10 to 25 × 10^9/L with minimal alterations in leukocyte composition.

Bordetella pertussis (Haemophilus pertussis) Infection

Whooping cough caused by B. pertussis leads to extensive respiratory tract inflammation.
Leukocyte counts can escalate to 100 × 10^9/L, with absolute lymphocyte values reaching 50 × 10^9/L, generally between 15 to 40 × 10^9/L.
Lymphocytes on blood smears are typically small and mature; definitive diagnosis is made by isolating the bacteria.

Lymphocytopenia

Defined as lymphocyte counts below 3.0 × 10^9/L in adults and below 1.5 × 10^9/L in children.
A reduction in lymphocytes often results from stress or corticosteroid use.
Transient relative lymphocytopenia correlates with conditions leading to granulocytosis.

Immune Disorders Associated with Lymphocytopenia

Immune disorders arise from defective numbers or functionalities of lymphocytes, which can be congenital or acquired.
Classifications can be made into T-cell or B-cell disorders, with some conditions impacting both cell types.

DiGeorge's Syndrome

Characterized by alterations in lymphocyte subpopulations; the condition displays a decrease in total T lymphocytes, increasing the ratio of helper T cells relative to suppressor T cells.

Acquired Immunodeficiency Syndrome (HIV/AIDS)

HIV is the primary virus responsible for AIDS.

Etiology

Initially identified in a homosexual man with lymphadenopathy, termed LAV.
The Gallo team then identified it as HTLV-III, eventually renaming it to HIV.
HIV targets the helper/inducer subset of T lymphocytes among other cell types, such as macrophages (40% of PB monocytes), lymph nodes, skin, and MALT tissue, and even a subset of B cells.

Epidemiology of HIV/AIDS

As of 2012, approximately 1.2 million individuals aged 13 and over were living with HIV in the US; 12.8% are undiagnosed but at risk.
In 2013, globally there were 2.1 million new cases and 1.5 million AIDS-related deaths.
The most affected regions include sub-Saharan Africa, along with increasing cases in parts of Asia, Europe, and Latin America.

Vulnerable Populations

Highest prevalence is found among:
- African Americans
- Gay and bisexual men (MSM) with 45%
- High-risk heterosexuals (27%)
- Injection drug users (22%)
- Combined MSM and IDU (5%)
Perinatal transmission is the predominant route for children's HIV infection, responsible for almost all AIDS cases among U.S. children.

Clinical Signs and Symptoms

Early stages: Mostly asymptomatic, slight chronic lymphadenopathy, or mild flu-like symptoms appear 2 weeks to 3 months post-infection.
Late phase: AIDS develops 8 to 9 years post-infection, with symptoms including severe weight loss, fever, and opportunistic infections leading to AIDS-defining malformations (like Kaposi’s sarcoma, and B-cell lymphomas).

Laboratory Data for AIDS Patients

Lymphocyte assessment focuses significantly on CD4+ lymphocyte counts, paired with leukopenia and lymphocytopenia observed.
A reversed CD4/CD8 ratio is seen in AIDS patients, with standard ratios of:
- Normal: 2:1 in heterosexuals; 1.5:1 in homosexuals
- AIDS cases: 0.5:1

Serological Markers: Detection of Viral Antigen

Post-infection, the immune response involves antibody development against viremia, although a window of seronegativity exists from 6 to 12 weeks post-infection.
EIA methods for antibodies against p41 become detectable before p24 antibodies appear positive.

Serological Markers: Antibodies to HIV-1

Antibodies to HIV-1 develop approximately 6 weeks after infection, but many false negatives occur if tested too soon.
Increased antibody titers for additional viruses (CMV, EBV, Hepatitis A and B, T. gondii) are also noted.

Other Immune Changes in HIV/AIDS

Patients experience polyclonal hypergammaglobulinemia, elevated interferon a, levels of a-1 thymosin, and b-microglobulin, along with decreased interleukin-1 and interleukin-2 levels.

Systemic Lupus Erythematosus (SLE)

An autoimmune disease affecting nearly all body organs, more common in females than males (8:1 ratio), typically diagnosed in adolescents or young adults.
Immunologically, SLE exhibits decreased total T cells and alterations among suppressor cell populations.

Clinical Symptoms of SLE

Symptoms to be aware of include:
- Fever
- Weight loss
- Malaise
- Arthralgia
- Arthritis
- Butterfly rash on the nose
- Kidney deterioration results due to immune complexes in the blood.

Laboratory Data for SLE

Outdated LE cell preparation may be noted, along with antibody tests and evaluations of lymphocyte subsets.

Antibody Tests in SLE

Common in SLE are antibodies targeting DNA (anti-nuclear antibodies, ANA), which can bind to nucleic acid molecules or proteins, assessed through either fluorescence or radioimmunoassays. The positive test threshold is typically greater than 1:32 antibody titer using either modality.

Lymphocyte Subsets in SLE

Disturbances among lymphocyte subsets are prominent in SLE:
- T-cell subpopulations exhibit reduced suppressor functions or elevated helper T cell production.
- B-cell hyperactivity leads to an increase in serum antibodies and autoantibodies, particularly IgG, resulting in the circulation of pathogenic immune complexes contributing to renal disease.