White blood cells - Immunity

White blood cells come in a number of varieties, each with specialized functions in the body. I mentioned before that they start out as lymphocytes - but really there are other specialized leukocytes (i.e. white blood cells) that aren't lymphocytes as well - specifically monocytes and the phils (neutrophils, eosinophils, basophils). Hematology (the study of the blood) is a field in its own right because of this complexity.

Scanning electron micrograph of blood

White blood cells are responsible for fighting infection and preventing invasion by foreign particles. They are constantly tasting the components in the blood to determine whether they belong to the body, and they do this through receptors on the cell surfaces. What happens if they find something that they don't recognize? An immune response.

Allergies are fast and severe immune responses to something the body doesn't recognize. This is why food intolerance can develop - slowly over time the immune cells become sensitive and then, bam, they're ready to attack and do. Allergies may also be due to the genetics of the proteins on the cell surfaces, which recognize certain food proteins as needing to react.

When the body lacks white blood cells, as in the case of HIV infection (the virus destroys the cells), immunodeficiency occurs. This makes the person susceptible to common infections. Normally we co-exist with bacteria, viruses, and fungi, like cytomegalovirus and strains of staph on our skin, but without the white blood cells to keep these pathogens in their place, they invade. Something as simple as the common cold can be deadly to a person with compromised immunity. And some people are born lacking the immunity they need - resulting in cases like that of the 'bubble boy' syndrome.

So now that we know the cell components of blood are important, what's the purpose of plasma? Read about that tomorrow.

Benign to malignant: Lymphadenopathy is a common symptom

Lymphadenopathy of the neck. Source: James Heilman, MD

 

Lymphadenopathy is the presence of enlarged lymph nodes, and it is often accompanied by tenderness, redness, and warmth at the location of the swollen node. This disorder can occur in a broad range of benign and malignant conditions, ranging from exposure to a virus to cancer. Lymph nodes are present throughout the body, mostly at points of entry and drainage in the lymph system, including the neck, groin, abdomen, and armpits. The lymph nodes filter the lymph (which contains excess tissue fluid and immune cells) as it circulates throughout the body, so swollen nodes indicate an active immune response. Depending on the cause, lymphadenopathy can be localized or generalized.

Normal lymph nodes

The human body contains hundreds of lymph nodes. Usually, the nodes below the jaw (i.e. submandibular), in the armpits (i.e. axillary), and the groin region (i.e. inguinal) can be felt in healthy adults. The lymph nodes contain a germinal center of B cells and macrophages. When an immune response is triggered, the germinal center enlarges with the replicating immune cells. Nodes larger than 1 cm in diameter are considered abnormal, though any knot or lump that appears may be indicative of lymphadenopathy. Clinicians have a standard evaluation technique they use to determine the extent and severity of enlargement, which eventually can aid in diagnosis. Children commonly have this condition due to their high exposure to “benign self-limited disease”, such as viruses. Essentially, some lymph node somewhere in the body is going to become enlarged for any immune reaction.

Localized lymphadenopathy

Localized lymphadenopathy is the most common form of lymph node swelling, occurring at a specific location on the body, either unilaterally or bilaterally (one side of the body versus both sides). The most common cause of localized lymph node swelling is a nearby lesion, such as strep throat causing cervical lymphadenopathy and an infection in an extremity leading to axillary or inguinal lymphadenopathy on the relevant side (the affected arm and leg, respectively). The most common lymph nodes to be enlarged are the cervical lymph nodes due to the exposure of the throat to inhaled and ingested pathogens. However, localized swelling of the supraclavicular lymph nodes may indicate malignancy, specifically the abdomen or chest if not present with generalized lymphadenopathy as noted in the clinician’s evaluation technique.

Generalized lymphadenopathy

Generalized lymphadenopathy is the enlargement of many lymph nodes at various points throughout the body. This is indicative of a systemic disorder. One example is a cancer of the immune system, called Hodgkin’s lymphoma, in which the lymph nodes enlarge much like tumor growth. HIV infection and metastatic cancer also cause a generalized immune response. Other diseases/disorders that cause a generalized response are tuberculosis, fungal infection, viral infection, connective tissue diseases, and autoimmune reactions.

Lymphadenitis

Lymphadenitis is inflammation of the lymph node, causing enlargement. This may be due to invasion of the lymph node by metabolite-laden macrophages or malignant cells. This form of enlargement is seen in lipid storage diseases. Infection of the lymph nodes (which can also lead to inflammation) is a common complication of many bacterial infections.

A new attack against HIV

The human immunodeficiency virus (HIV) encodes vif, a virulence factor that deactivates the enzyme APOBEC-3G. This enzyme may be the key to the body's natural defense against HIV. A new study published in Nature discerning the crystal structure of the enzyme may be one of the first to show the potential of blocking vif and allowing APOBEC-3G to attack HIV in the fight against the ongoing epidemic of AIDS. The enzyme blocks HIV replication and, if vif is prevented from acting, the enzyme will continue to prevent HIV from causing AIDS. Knowing the structure of the enzyme will aid the development of drugs that prevent vif from binding.