The aim of the study was to investigate whether normal aging leads to blood cells being produced from fewer cell clones. This was examined by comparing which X chromosome the cells were using between different age groups and between neutrophils and T cells.

In other words, they studied human hematopoiesis across age by analyzing purified blood cell lineages from the subjects.

Modell/material
- 197 hematologically normal females
	- 23 new born
	- 94 young adult (median 30)
	- 80 eldery (over 75)
- purified neutrofils
- purified T-cells

**Methods**

1. Peripheral blood samples were collected
2. Neutrophils and T cells were isolated using cell separation techniques _(centrifugation followed by lineage-specific purification)_
3. X-chromosome inactivation was analyzed using the HUMARA PCR assay _(PCR-based measurement of which X chromosome is active)_
4. T cells were analyzed by PCR to check for clonal expansion _(T-cell receptor γ gene rearrangement analysis)_
### Results
1. X chromosome usage is similar in newborns and young adults.
2. Neutrophils from elderly individuals show strongly uneven X chromosome usage.
3. T-cells show much less uneven X chromosome usage and no dominant clonal expansion

### Figure
![[image-183.png|177x186]] 
Notes
- This graph shows the distribution of X chromosome usage in 23 newborn females
- X-axis: the % of cells using the less common X chromosome.
	- 50% means perfectly (50% maternal / 50% paternal)
	- 0/100% means all cells use the same chromosome
- Y-axis: number of individuals in each group

Conclusion: 
- Newborns mostly show balanced use of the two X chromosomes.

![[image-184.png|177x193]]
Notes
- This graph shows the purified neutrofils from 80 elderly (y >= 75) females
- X and Y axis is the same as in previous graph

Conclusion:
- Elderly neutrophils frequently show strongly uneven X chromosome usage.