Lymphocytes play a fundamental role in the immune process. They are involved in the genesis and maintenance of most systemic conditions; their quantitative and qualitative deficiency contributes to the weakening of humoral and cellular expenses.
Originating in the bone marrow, differentiated B and T lymphocytes, they are carriers of antigenic specificities can be identified by the laboratory, including flow cytometry. A cascade of biological events, recognition of an antigen, producing messages (cytokines), development of antibodies, specific cellular defense processes, characterizes the different phases of an immune response that should be neither poor nor exaggerated or unnecessarily prolonged.
The mature T cells, the antigen receptor is associated with the CD3 marker differentiate in the thymus:Schematically, mature B cells carry a surface immunoglobulin specific antigen receptor, which will allow B cells to proliferate and differentiate to the stage of plasma cells secreting antibodies.
– T helper expressing CD4;
– T suppressor CD8 expressing.
In the circulation, the majority of lymphocytes (70-80%) are T cells which two thirds and one third of CD4 CD8; B cells represent about 20% of the lymphoid population.
Immune deficiencies may relate to cellular immunity, they are usually accompanied by a T cell lymphopenia essentially deficits in humoral immunity, carried by B cells, are associated mainly to a decrease of immunoglobulins .
Some are combined deficits on both lines B and T. In addition abnormalities in T helper or suppressor populations are responsible for the B maturation disorders and abnormalities of the humoral response.
Lymphopenia, defined by a figure of less than 1,000 cells / mm3 in adults and less than 3000 / mm3 in children less than two years, can not be separated from her clinic and immunohematological context. It may reflect a constitutional immune disorder, rare genetic recessive or dominant inheritance, autosomal or sex-linked in infancy may result in major infectious problem.
Lymphopenia can also integrate with acquired immunodeficiency whose most frequent causes of cancer chemotherapy and immunosuppressive infection with HIV (HIV).
The exploration is based primarily on the clinical setting, playback and control of blood counts.
The patient’s age, personal and family history, discovering the circumstances, symptoms, examination forming organs often allow a first orientation to a constitutional or acquired disorder, transient or chronic.
With no obvious cause immunosuppressive, finding infection, lymphoid pathology, a systemic disease will be made.
Biologically, the strict hematological investigations will be conducted according to the clinical assessment and blood counts: viral and retroviral serology, immunoglobulin assays, studies on lymphocyte populations and in very special settings, functional study of lymphocytes by specialized laboratories.
The main causes of these deficits with lymphopenia are:
– The suppression of lymphoid stem cells;
– The severe combined immunodeficiency, possibly associated with an adenosine deaminase deficiency;
– The combined partial achievement of B and T cells;
– Wiscott Aldrich syndrome: related to sex, he strikes male infants with eczema, thrombocytopenia, IgM deficiency, recurrent infections;
– Ataxia telangiectasia;
– The isolated deficiency of T cells: Di syndrome
Gorge with thymic hypoplasia;
– The isolated deficiency of B cells:
– Bruton’s disease, recessive overall deficit related to sex with a child male agammaglobulinemia, an absence of B lymphocytes and plasma cells, transient hypogammaglobulinemia of the infant.
They are as follows:
– Pyogenic infections during severe hypogammaglobulinemia;
– Viral infections, BCGitis, fungal infections;
– Autoimmune events (severe combined immunodeficiency) and malignant lymphoid proliferation.
Depending on the type and severity of the consequences of the deficit, the treatment will be based on specific antibiotics, infusions of immunoglobulins or allograft in combined deficits conducted among children living in a protected atmosphere (“bubbles” sterile).
AIDS is defi ned in a HIV positive patient usually having a CD4 count below 200 / mm3, by the occurrence of opportunistic infections associated with deficiency of cellular immunity, or a malignant proliferation: sarcoma sarcoma, lymphoma, genital cancer, or HIV-related dementia.
These events are still indicative of infection in many cases. We quote pneumocystosis, cerebral toxoplasmosis, candidiasis, cryptosporidiosis, cytomegalovirus infection, atypical mycobacterial infections.
The clinical and epidemiological context, the CBC, the practice of a serology HIV 1 and 2, the lymphocyte typing CD4 / CD8, measuring viral load (number of RNA copies), can confirm the diagnosis and initiate codified antiretroviral treatment that restores cellular immunity today.
During the evolution that becomes chronic, monitoring the CD4 count is a major parameter. A rate below 200 / mm3 requires continuous prevention of opportunistic infections in particular by Bactrim®.
When the CD4 lymphocytes rate rises under triple therapy, and if the patient has an opportunistic infection (especially mycobacteriosis), may occur with immune restoration syndrome.
Other causes of lymphopenia acquired:
They are as follows:
– Immunosuppressive therapy, radiotherapy;
– Malignant lymphoid blood diseases: lymphatic leukemia, Hodgkin’s disease, non-Hodgkin lymphoma;
– Infectious diseases including mycobacteria tuberculosis, leprosy; viral infections;
– Autoimmune attacks and / or disorders: systemic lupus erythematosus, sarcoidosis;
– Undernutrition; senescence; zinc deficiency; digestive malabsorption.
Idiopathic CD4 lymphopenia:
Since 1990 has been recognized chronic idiopathic CD4 lymphopenia, immune deficiency in young adults that could be observed in 1% of the adult population and be complicated by severe opportunistic infections. Familial cases have been reported rarely and an evolution towards malignant lymphomas.
The diagnosis can be suspected in an adult under 75 years on the occasion of a systematic blood count or an opportunistic infection with controlled three-month rate of CD4 T cells below 300 / mm3 or below 20% T cells, in the absence of an HIV infection or other lymphopenic virus, immunosuppressive therapy, or starvation.
Studies are underway to determine the abnormalities or T cell activation mechanisms that can be retained in a clinico-biological context probably heterogeneous.
The management of these patients is based on regular clinical and hematological monitoring, treatment and prevention of opportunistic infections, in some cases treatment with interleukin-2.