Depression is one of the most burdensome psychiatric conditions having atleast five of the symptoms occurring most of the day, nearly every day for past two weeks as mentioned in ICD-11 criteria.¹ As per ICD 11, depressive episodes are classified based severity and associated psychotic symptoms as (a) mild depressive episode, (b) moderate depressive episode without psychotic symptoms, (c) moderate depressive episode with psychotic symptoms, (d) Severe depressive episode without psychotic symptoms and (e) severe depressive episode with psychotic symptoms.¹ It has been studied that 1 in 40 persons have history of depression in the past, 1 in 20 persons suffer from current depression and 0.9 % of population have high self-injury and suicide risk.² There are many etiologic factors that causes depression e.g., stressful life events, early maladaptive schema, genetic, hormonal,  Immune dysfunction, etc.³ Alteration in innate and adaptive immune status affects the prognosis and action of antidepressant.³ IL-6 and TNF alpha are elevated in acute depressive episode and are decreased after treatment.⁴ Th17 cells are increased in patients showing non- responsiveness to antidepressant therapy.⁴ Peripheral T-cells are responsible for neuroplasticity and plays a role in both the development and resolution of depression.⁵ Neurogenic stress induced in the body alters the permeability of the blood brain barrier resulting in entry of peripheral cytokines to brain causing mood disorder.⁵ Depression itself disturbs the Hypothalamo-Pituitary-Adrenal axis and autonomic nervous system which induces production of more cytokines worsening the symptoms.⁶ The drug of choice for the patients with major depressive disorder (MDD) were Tricyclic anti-depressants previously.⁷ But, now Selective serotonin reuptake inhibitors (SSRI) and atypical antidepressants has become the choice.^7-8 Despite the advancement in treatment options, one third of patient develops treatment resistance.⁹ However, there is hardly any method to know among the patients who is going to develop Treatment Resistant Depression (TRD). This will be an attempt to find out if CD4⁺ T-cell count and its subsets alter in MDD and can differentiate Treatment Resistant Depression (TRD) and non-Treatment Resistant Depression at the time of presentation. This study will also assess if immune status of MDD patient with tendency for self-injury and suicide differs from those MDD patients without having those tendency.