Viral Infection: Many viral infections can cause a decrease in white blood cell count (leukopenia) with a relative lymphocytosis. The body's response to viral infections often involves an increase in lymphocytes, which are crucial for fighting off viruses. Basophils may also be mildly elevated in some cases due to the inflammatory response.

Chronic Inflammatory Conditions: Conditions like rheumatoid arthritis or chronic obstructive pulmonary disease (COPD) can lead to a chronic inflammatory state, which may result in a mild elevation of lymphocytes and basophils alongside a low WBC count due to the body's ongoing immune response.
Medication Side Effects: Certain medications, including some antibiotics, anticonvulsants, and chemotherapeutic agents, are known to cause leukopenia as a side effect. The effect on lymphocytes and basophils can vary, but some may induce a mild increase in these cell lines.
Hypersplenism: This condition, characterized by an overactive spleen, can lead to the sequestration of white blood cells, resulting in a low WBC count. Lymphocytes and basophils might be relatively spared or mildly elevated, depending on the underlying cause of hypersplenism.

Leukemia or Lymphoma: Although less common, it's crucial not to miss diagnoses like leukemia or lymphoma, which can present with abnormal white blood cell counts, including low WBC with elevated lymphocytes. Basophils might also be affected in certain types of leukemia.
Aplastic Anemia: This is a rare, potentially life-threatening failure of bone marrow activity, which can result in a decrease in all blood cell types, including white blood cells. Early detection is critical for treatment.
Severe Chronic Diseases: Conditions like severe renal failure or liver disease can affect the bone marrow's ability to produce blood cells, leading to abnormalities in the WBC count, including a decrease with relative lymphocytosis and basophilia.

Myeloproliferative Neoplasms (MPN): Certain MPNs, like chronic myeloid leukemia (CML), can present with basophilia. However, these conditions more commonly cause an elevation in WBC count rather than a decrease.
Congenital Immunodeficiencies: Rare genetic disorders that affect the immune system can lead to abnormalities in white blood cell counts, including low WBC counts with specific patterns of lymphocyte and basophil elevation.
Paroxysmal Nocturnal Hemoglobinuria (PNH): A rare, acquired, life-threatening disease of the blood characterized by the destruction of red blood cells, bone marrow failure, and the potential for blood clot formation. It can present with various cytopenias, including leukopenia.