Reactive lymphocytes


Reactive lymphocytes

When we see reactive lymphocytes we tend to think of responses to virus. However, in reality there are a number of different reactive responses:

1. Reactive states characterised by highly variable forms:

  • Viral reaction (typified by EBV infection), may be characterised by flamboyant and varied forms
  • Lymphocytosis with a less activated appearance may also be seen in a range of disorders that include infection, inflammation or neoplasia
  • Generally a slide test for glandular fever will be performed, thereafter a decision on further investigation should be made

EBV infection
Appearances can range from very large cells with deeply blue cytoplasm (sometimes the basophilia is more peripheral), a large primitive nucleus, and a tendency to enfold their cytoplasm around red cells. Some cells may resemble monocytes, while others are irregular, lymphoplasmacytoid or even normal. This variability is a useful indicator of reactive lymphocytes.

Where the cause is viral, the apoptosis of infected B cells may also be seen, this is a useful (though not absolutely specific) confirmation of diagnosis:

Activated T cells with apoptotic B cells
Large reactive lymphocytes in viral disease are often cytotoxic T cells. These are responsible for inducing apoptosis of virally infected B cells - in some cases the apoptotic (condensed, vacuolated and blebbed) infected B cells can be seen on the blood film

2. Reactive states characterised by increased counts of small (often clefted) lymphocytes:

  • This is best shown by the reactive increase associated with Bordetella pertussis infection (whooping cough)
  • These most commonly arise in children or young adults
  • They can arise in a range of conditions however, the cause should be sought

Small reactive T cells
In this case the small clefted and reactive cells arose in the context of a bone marrow transplant and viral infection - they could easily represent a neoplastic population based on morphology alone

3. Reactive states associated with predominantly LGL type cells:

  • Reactive conditions in autoimmune states or immune activation with predominantly LGL type cells: autoimmune (particularly rheumatoid disease), bone marrow transplant, viral.
  • Note that morphology alone cannot distinguish reactive from neoplastic LGL cells - if clinically atypical, the count is sustained, or with high count (>0.4x109/l) then LGL proliferations should be considered (see T and NK cell disorders)